diff --git a/common/CMakeLists.txt b/common/CMakeLists.txt
index 08e50f575b..0883e764f2 100644
--- a/common/CMakeLists.txt
+++ b/common/CMakeLists.txt
@@ -398,6 +398,7 @@ set( COMMON_SRCS
     settings/common_settings.cpp
     settings/json_settings.cpp
     settings/nested_settings.cpp
+    settings/project_file.cpp
     settings/settings_manager.cpp
 
     libeval/numeric_evaluator.cpp
diff --git a/common/project.cpp b/common/project.cpp
index e44290b5bc..61f24b6f38 100644
--- a/common/project.cpp
+++ b/common/project.cpp
@@ -92,7 +92,7 @@ void PROJECT::SetProjectFullName( const wxString& aFullPathAndName )
 
         wxASSERT( m_project_name.IsAbsolute() );
 
-        wxASSERT( m_project_name.GetExt() == ProjectFileExtension );
+        wxASSERT( m_project_name.GetExt() == LegacyProjectFileExtension );
 
         // until multiple projects are in play, set an environment variable for the
         // the project pointer.
@@ -279,7 +279,7 @@ static bool copy_pro_file_template( const SEARCH_STACK& aSearchS, const wxString
         return false;
     }
 
-    wxString templateFile = wxT( "kicad." ) + ProjectFileExtension;
+    wxString templateFile = wxT( "kicad." ) + LegacyProjectFileExtension;
 
     wxString kicad_pro_template = aSearchS.FindValidPath( templateFile );
 
@@ -289,7 +289,7 @@ static bool copy_pro_file_template( const SEARCH_STACK& aSearchS, const wxString
                     __func__, TO_UTF8( templateFile ) );
 
         wxFileName  templ( wxStandardPaths::Get().GetDocumentsDir(),
-                            wxT( "kicad" ), ProjectFileExtension );
+                            wxT( "kicad" ), LegacyProjectFileExtension );
 
         if( !templ.IsFileReadable() )
         {
diff --git a/common/settings/json_settings.cpp b/common/settings/json_settings.cpp
index 48b91ae5dd..5b964f589b 100644
--- a/common/settings/json_settings.cpp
+++ b/common/settings/json_settings.cpp
@@ -84,14 +84,16 @@ void JSON_SETTINGS::Load()
 }
 
 
-void JSON_SETTINGS::LoadFromFile( const std::string& aDirectory )
+bool JSON_SETTINGS::LoadFromFile( const std::string& aDirectory )
 {
     // First, load all params to default values
     clear();
     Load();
 
-    bool      migrated        = false;
-    bool      legacy_migrated = false;
+    bool success         = true;
+    bool migrated        = false;
+    bool legacy_migrated = false;
+
     LOCALE_IO locale;
 
     auto migrateFromLegacy = [&] ( wxFileName& aPath ) {
@@ -114,12 +116,22 @@ void JSON_SETTINGS::LoadFromFile( const std::string& aDirectory )
         legacy_migrated = true;
     };
 
-    wxFileName path( aDirectory, m_filename, "json" );
+    wxFileName path;
+
+    if( aDirectory.empty() )
+    {
+        path.Assign( m_filename );
+        path.SetExt( wxT( "json" ) );
+    }
+    else
+    {
+        path.Assign( aDirectory, m_filename, wxT( "json" ) );
+    }
 
     if( !path.Exists() )
     {
         // Case 1: legacy migration, no .json extension yet
-        path.ClearExt();
+        path.SetExt( getLegacyFileExt() );
 
         if( path.Exists() )
         {
@@ -133,6 +145,10 @@ void JSON_SETTINGS::LoadFromFile( const std::string& aDirectory )
             if( path.Exists() )
                 migrateFromLegacy( path );
         }
+        else
+        {
+            success = false;
+        }
     }
     else
     {
@@ -151,6 +167,7 @@ void JSON_SETTINGS::LoadFromFile( const std::string& aDirectory )
             catch( ... )
             {
                 wxLogTrace( traceSettings, "%s: file version could not be read!", m_filename );
+                success = false;
             }
 
             if( filever >= 0 && filever < m_schemaVersion )
@@ -204,6 +221,8 @@ void JSON_SETTINGS::LoadFromFile( const std::string& aDirectory )
         // And write-out immediately so that we don't lose data if the program later crashes.
         SaveToFile( aDirectory );
     }
+
+    return success;
 }
 
 
@@ -233,7 +252,17 @@ bool JSON_SETTINGS::SaveToFile( const std::string& aDirectory, bool aForce )
     if( !m_writeFile )
         return false;
 
-    wxFileName path( aDirectory, m_filename, "json" );
+    wxFileName path;
+
+    if( aDirectory.empty() )
+    {
+        path.Assign( m_filename );
+        path.SetExt( wxT( "json" ) );
+    }
+    else
+    {
+        path.Assign( aDirectory, m_filename, wxT( "json" ) );
+    }
 
     if( !m_createIfMissing && !path.FileExists() )
     {
diff --git a/common/settings/nested_settings.cpp b/common/settings/nested_settings.cpp
index 29179afe4a..c685a7e895 100644
--- a/common/settings/nested_settings.cpp
+++ b/common/settings/nested_settings.cpp
@@ -46,9 +46,10 @@ NESTED_SETTINGS::~NESTED_SETTINGS()
 }
 
 
-void NESTED_SETTINGS::LoadFromFile( const std::string& aDirectory )
+bool NESTED_SETTINGS::LoadFromFile( const std::string& aDirectory )
 {
     clear();
+    bool success = false;
 
     if( m_parent )
     {
@@ -58,6 +59,8 @@ void NESTED_SETTINGS::LoadFromFile( const std::string& aDirectory )
 
             wxLogTrace( traceSettings, "Loaded NESTED_SETTINGS %s with schema %d", GetFilename(),
                     m_schemaVersion );
+
+            success = true;
         }
         catch( ... )
         {
@@ -67,6 +70,8 @@ void NESTED_SETTINGS::LoadFromFile( const std::string& aDirectory )
     }
 
     Load();
+
+    return success;
 }
 
 
diff --git a/common/settings/project_file.cpp b/common/settings/project_file.cpp
new file mode 100644
index 0000000000..0751d73eb3
--- /dev/null
+++ b/common/settings/project_file.cpp
@@ -0,0 +1,135 @@
+/*
+ * This program source code file is part of KiCad, a free EDA CAD application.
+ *
+ * Copyright (C) 2020 CERN
+ * @author Jon Evans <jon@craftyjon.com>
+ *
+ * This program is free software: you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License as published by the
+ * Free Software Foundation, either version 3 of the License, or (at your
+ * option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include <config_params.h>
+#include <settings/common_settings.h>
+#include <settings/parameters.h>
+#include <settings/project_file.h>
+#include <wildcards_and_files_ext.h>
+#include <wx/config.h>
+#include <wx/log.h>
+
+extern const char* traceSettings;
+
+///! Update the schema version whenever a migration is required
+const int projectFileSchemaVersion = 1;
+
+
+PROJECT_FILE::PROJECT_FILE( const std::string& aFullPath ) :
+        JSON_SETTINGS( aFullPath, SETTINGS_LOC::NONE, projectFileSchemaVersion ),
+        m_sheets(), m_boards(), m_legacyVars()
+{
+    m_params.emplace_back( new PARAM_LIST<FILE_INFO_PAIR>( "sheets", &m_sheets, {} ) );
+
+    m_params.emplace_back( new PARAM_LIST<FILE_INFO_PAIR>( "boards", &m_boards, {} ) );
+
+    m_params.emplace_back( new PARAM_MAP<wxString>( "legacy", &m_legacyVars, {} ) );
+}
+
+
+bool PROJECT_FILE::MigrateFromLegacy( wxConfigBase* aLegacyFile )
+{
+    bool     ret = true;
+    wxString str;
+    long     dummy;
+
+    // Legacy files don't store board info; they assume board matches project name
+    // We will leave m_boards empty here so it can be populated with other code
+
+    auto loadSheetNames =
+            [&]() -> bool
+            {
+                int index = 1;
+                wxString entry;
+
+                aLegacyFile->SetPath( GROUP_SHEET_NAMES );
+
+                while( aLegacyFile->Read( wxString::Format( "%d", index++ ), &entry ) )
+                {
+                    wxArrayString tokens = wxSplit( entry, ':' );
+
+                    if( tokens.size() == 2 )
+                        m_sheets.emplace_back( std::make_pair( KIID( tokens[0] ), tokens[1] ) );
+                }
+
+                // TODO: any reason we want to fail on this?
+                return true;
+            };
+
+    std::vector<wxString> groups;
+
+    bool more = aLegacyFile->GetFirstGroup( str, dummy );
+
+    while( more )
+    {
+        if( str == GROUP_SHEET_NAMES )
+            ret |= loadSheetNames();
+        else
+            groups.emplace_back( str );
+
+        more = aLegacyFile->GetNextGroup( str, dummy );
+    }
+
+    auto loadLegacyPairs =
+            [&]( const wxString& aGroup = wxEmptyString ) -> bool
+            {
+                aLegacyFile->SetPath( aGroup );
+
+                bool morePairs = aLegacyFile->GetFirstEntry( str, dummy );
+
+                while( morePairs )
+                {
+                    wxString    val = aLegacyFile->Read( str );
+                    std::string key( str.ToUTF8() );
+                    m_legacyVars[key] = val;
+                    morePairs         = aLegacyFile->GetNextEntry( str, dummy );
+                }
+
+                // TODO: any reason we want to fail on this?
+                return true;
+            };
+
+    ret &= loadLegacyPairs();
+
+    for( const auto& groupName : groups )
+        ret &= loadLegacyPairs( groupName );
+
+    return ret;
+}
+
+
+wxString PROJECT_FILE::getLegacyFileExt() const
+{
+    return LegacyProjectFileExtension;
+}
+
+
+void to_json( nlohmann::json& aJson, const FILE_INFO_PAIR& aPair )
+{
+    aJson = nlohmann::json::array( { aPair.first.AsString().ToUTF8(), aPair.second.ToUTF8() } );
+}
+
+
+void from_json( const nlohmann::json& aJson, FILE_INFO_PAIR& aPair )
+{
+    wxASSERT( aJson.is_array() && aJson.size() == 2 );
+    aPair.first  = KIID( wxString( aJson[0].get<std::string>().c_str(), wxConvUTF8 ) );
+    aPair.second = wxString( aJson[1].get<std::string>().c_str(), wxConvUTF8 );
+}
\ No newline at end of file
diff --git a/common/settings/settings_manager.cpp b/common/settings/settings_manager.cpp
index 68540d5026..65d00a718c 100644
--- a/common/settings/settings_manager.cpp
+++ b/common/settings/settings_manager.cpp
@@ -29,10 +29,12 @@
 #include <dialogs/dialog_migrate_settings.h>
 #include <gestfich.h>
 #include <macros.h>
+#include <project.h>
 #include <settings/app_settings.h>
-#include <settings/common_settings.h>
-#include <settings/settings_manager.h>
 #include <settings/color_settings.h>
+#include <settings/common_settings.h>
+#include <settings/project_file.h>
+#include <settings/settings_manager.h>
 
 
 /**
@@ -330,6 +332,9 @@ std::string SETTINGS_MANAGER::GetPathForSettingsFile( JSON_SETTINGS* aSettings )
     case SETTINGS_LOC::COLORS:
         return GetColorSettingsPath();
 
+    case SETTINGS_LOC::NONE:
+        return "";
+
     default:
         wxASSERT_MSG( false, "Unknown settings location!" );
     }
@@ -654,3 +659,49 @@ bool SETTINGS_MANAGER::extractVersion( const std::string& aVersionString, int* a
 
     return false;
 }
+
+
+bool SETTINGS_MANAGER::LoadProject( PROJECT& aProject )
+{
+    wxString name = aProject.GetProjectFullName();
+    std::string fn( name.ToUTF8() );
+
+    // Unload if already loaded
+    if( m_project_files.count( name ) )
+        UnloadProject( aProject );
+
+    PROJECT_FILE* file =
+            static_cast<PROJECT_FILE*>( RegisterSettings( new PROJECT_FILE( fn ), false ) );
+
+    m_project_files[aProject.GetProjectFullName()] = file;
+
+    return file->LoadFromFile();
+}
+
+
+bool SETTINGS_MANAGER::UnloadProject( PROJECT& aProject )
+{
+    wxString name = aProject.GetProjectFullName();
+
+    if( !m_project_files.count( name ) )
+        return false;
+
+    PROJECT_FILE* file = m_project_files[name];
+
+    auto it = std::find_if( m_settings.begin(), m_settings.end(),
+                            [&file]( const std::unique_ptr<JSON_SETTINGS>& aPtr )
+                            {
+                              return aPtr.get() == file;
+                            } );
+
+    if( it != m_settings.end() )
+    {
+        wxLogTrace( traceSettings, "Unload project %s", ( *it )->GetFilename() );
+        ( *it )->SaveToFile();
+        m_settings.erase( it );
+    }
+
+    m_project_files.erase( name );
+
+    return true;
+}
diff --git a/common/wildcards_and_files_ext.cpp b/common/wildcards_and_files_ext.cpp
index 44068d9e80..e7d34a4e91 100644
--- a/common/wildcards_and_files_ext.cpp
+++ b/common/wildcards_and_files_ext.cpp
@@ -120,7 +120,8 @@ const std::string LegacySymbolLibFileExtension( "lib" );
 
 const std::string VrmlFileExtension( "wrl" );
 
-const std::string ProjectFileExtension( "pro" );
+const std::string ProjectFileExtension( "kicad_pro" );
+const std::string LegacyProjectFileExtension( "pro" );
 const std::string LegacySchematicFileExtension( "sch" );
 const std::string KiCadSchematicFileExtension( "kicad_sch" );
 const std::string NetlistFileExtension( "net" );
diff --git a/eeschema/dialogs/dialog_sch_import_settings.cpp b/eeschema/dialogs/dialog_sch_import_settings.cpp
index 0cf5b11129..9b2bd28463 100644
--- a/eeschema/dialogs/dialog_sch_import_settings.cpp
+++ b/eeschema/dialogs/dialog_sch_import_settings.cpp
@@ -56,7 +56,7 @@ bool DIALOG_SCH_IMPORT_SETTINGS::TransferDataToWindow()
 void DIALOG_SCH_IMPORT_SETTINGS::OnBrowseClicked( wxCommandEvent& event )
 {
     wxFileName fn = m_frame->Schematic().Root().GetFileName();
-    fn.SetExt( ProjectFileExtension );
+    fn.SetExt( LegacyProjectFileExtension );
 
     wxFileDialog dlg( this, _( "Import Settings From" ), fn.GetPath(), fn.GetFullName(),
                       ProjectFileWildcard(), wxFD_OPEN | wxFD_FILE_MUST_EXIST | wxFD_CHANGE_DIR );
diff --git a/eeschema/eeschema_config.cpp b/eeschema/eeschema_config.cpp
index 0347d88118..ca477d2b71 100644
--- a/eeschema/eeschema_config.cpp
+++ b/eeschema/eeschema_config.cpp
@@ -369,7 +369,7 @@ void SCH_EDIT_FRAME::SaveProjectSettings()
     PROJECT&        prj = Prj();
     wxFileName      fn = Schematic().RootScreen()->GetFileName();  //ConfigFileName
 
-    fn.SetExt( ProjectFileExtension );
+    fn.SetExt( LegacyProjectFileExtension );
 
     if( !fn.HasName() || !IsWritable( fn ) )
         return;
diff --git a/eeschema/files-io.cpp b/eeschema/files-io.cpp
index ed114c0b3b..1d2763736e 100644
--- a/eeschema/files-io.cpp
+++ b/eeschema/files-io.cpp
@@ -260,7 +260,7 @@ bool SCH_EDIT_FRAME::OpenProjectFiles( const std::vector<wxString>& aFileSet, in
         return false;
 
     wxFileName pro = fullFileName;
-    pro.SetExt( ProjectFileExtension );
+    pro.SetExt( LegacyProjectFileExtension );
 
     bool is_new = !wxFileName::IsFileReadable( fullFileName );
 
@@ -605,7 +605,7 @@ void SCH_EDIT_FRAME::OnImportProject( wxCommandEvent& aEvent )
     if( setProject )
     {
         wxFileName projectFn( dlg.GetPath() );
-        projectFn.SetExt( ProjectFileExtension );
+        projectFn.SetExt( LegacyProjectFileExtension );
         Prj().SetProjectFullName( projectFn.GetFullPath() );
     }
 
diff --git a/include/settings/json_settings.h b/include/settings/json_settings.h
index 71c64c87cf..172ba736c7 100644
--- a/include/settings/json_settings.h
+++ b/include/settings/json_settings.h
@@ -38,6 +38,7 @@ enum class SETTINGS_LOC {
     PROJECT,    ///< The settings directory inside a project folder
     COLORS,     ///< The color scheme directory (e.g. ~/.config/kicad/colors/)
     NESTED,     ///< Not stored in a file, but inside another JSON_SETTINGS
+    NONE,       ///< No directory prepended, full path in filename (used for PROJECT_FILE)
 };
 
 
@@ -73,8 +74,9 @@ public:
     /**
      * Loads the backing file from disk and then calls Load()
      * @param aDirectory is the path to the file
+     * @return true if the file was found on disk and loaded or migrated
      */
-    virtual void LoadFromFile( const std::string& aDirectory );
+    virtual bool LoadFromFile( const std::string& aDirectory = "" );
 
     /**
      * Calls Store() and then writes the contents of the JSON document to a file
@@ -82,7 +84,7 @@ public:
      * @param aForce if true will always save, even if contents are not modified
      * @return true if the file was saved
      */
-    virtual bool SaveToFile( const std::string& aDirectory, bool aForce = false );
+    virtual bool SaveToFile( const std::string& aDirectory = "", bool aForce = false );
 
     /**
      * Resets all parameters to default values.  Does NOT write to file or update underlying JSON.
@@ -211,6 +213,11 @@ protected:
     bool fromLegacyColor( wxConfigBase* aConfig, const std::string& aKey,
                           const std::string& aDest );
 
+    virtual wxString getLegacyFileExt() const
+    {
+        return wxEmptyString;
+    }
+
     /// The filename (not including path) of this settings file
     std::string m_filename;
 
diff --git a/include/settings/nested_settings.h b/include/settings/nested_settings.h
index a500bf09c3..203099c57d 100644
--- a/include/settings/nested_settings.h
+++ b/include/settings/nested_settings.h
@@ -40,7 +40,7 @@ public:
      * Loads the JSON document from the parent and then calls Load()
      * @param aDirectory
      */
-    void LoadFromFile( const std::string& aDirectory = "" ) override;
+    bool LoadFromFile( const std::string& aDirectory = "" ) override;
 
     /**
      * Calls Store() and then saves the JSON document contents into the parent JSON_SETTINGS
diff --git a/include/settings/project_file.h b/include/settings/project_file.h
new file mode 100644
index 0000000000..8e349ed6bf
--- /dev/null
+++ b/include/settings/project_file.h
@@ -0,0 +1,79 @@
+/*
+ * This program source code file is part of KiCad, a free EDA CAD application.
+ *
+ * Copyright (C) 2020 CERN
+ * @author Jon Evans <jon@craftyjon.com>
+ *
+ * This program is free software: you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License as published by the
+ * Free Software Foundation, either version 3 of the License, or (at your
+ * option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#ifndef KICAD_PROJECT_FILE_H
+#define KICAD_PROJECT_FILE_H
+
+#include <common.h>
+#include <settings/json_settings.h>
+
+
+/**
+ * For files like sheets and boards, a pair of that object KIID and display name
+ * Display name is typically blank for the project root sheet
+ */
+typedef std::pair<KIID, wxString> FILE_INFO_PAIR;
+
+
+/**
+ * PROJECT_FILE is the backing store for a PROJECT, in JSON format.
+ *
+ * There is either zero or one PROJECT_FILE for every PROJECT
+ * (you can have a dummy PROJECT that has no file)
+ */
+class PROJECT_FILE : public JSON_SETTINGS
+{
+public:
+    /**
+     * Constructs the project file for a project
+     * @param aFullPath is the full disk path to the project
+     */
+    PROJECT_FILE( const std::string& aFullPath );
+
+    virtual ~PROJECT_FILE() {}
+
+    virtual bool MigrateFromLegacy( wxConfigBase* aLegacyFile ) override;
+
+protected:
+    wxString getLegacyFileExt() const override;
+
+private:
+
+    /// An list of schematic sheets in this project
+    std::vector<FILE_INFO_PAIR> m_sheets;
+
+    /// A list of board files in this project
+    std::vector<FILE_INFO_PAIR> m_boards;
+
+    /**
+     * Stores all K/V pairs migrated from a legacy (.pro) file so that the legacy file can be
+     * removed before these settings are migrated in by PROJECT_SETTINGS objects later.
+     */
+    std::map<std::string, wxString> m_legacyVars;
+
+};
+
+// Specializations to allow directly reading/writing FILE_INFO_PAIRs from JSON
+
+void to_json( nlohmann::json& aJson, const FILE_INFO_PAIR& aPair );
+
+void from_json( const nlohmann::json& aJson, FILE_INFO_PAIR& aPair );
+
+#endif
diff --git a/include/settings/settings_manager.h b/include/settings/settings_manager.h
index 7ff763d887..86488b6694 100644
--- a/include/settings/settings_manager.h
+++ b/include/settings/settings_manager.h
@@ -26,6 +26,8 @@
 
 class COLOR_SETTINGS;
 class COMMON_SETTINGS;
+class PROJECT;
+class PROJECT_FILE;
 
 
 class SETTINGS_MANAGER
@@ -179,6 +181,20 @@ public:
      */
     void ReloadColorSettings();
 
+    /**
+     * Registers a project and attempts to load the associated PROJECT_FILE
+     * @param aProject is the project object to load
+     * @return true if the PROJECT_FILE was successfully loaded
+     */
+    bool LoadProject( PROJECT& aProject );
+
+    /**
+     * Saves, unloads and unregisters the given project
+     * @param aProject is the project object to unload
+     * @return true if the PROJECT file was successfully saved
+     */
+    bool UnloadProject( PROJECT& aProject );
+
     /**
      * Checks if a given path is probably a valid KiCad configuration directory.
      * Actually it just checks if a file called "kicad_common" exists, because that's probably
@@ -269,6 +285,12 @@ private:
 
     /// True if settings loaded successfully at construction
     bool m_ok;
+
+    /// Project files, mapped according to project full name
+    std::map<wxString, PROJECT_FILE*> m_project_files;
+
+    /// A list of project settings objects for each loaded project
+    // std::map<wxString, std::vector<PROJECT_SETTINGS*>> m_project_settings;
 };
 
 #endif
diff --git a/include/wildcards_and_files_ext.h b/include/wildcards_and_files_ext.h
index 234396d2c2..88d189537f 100644
--- a/include/wildcards_and_files_ext.h
+++ b/include/wildcards_and_files_ext.h
@@ -115,6 +115,7 @@ extern const std::string SchematicBackupFileExtension;
 
 extern const std::string VrmlFileExtension;
 extern const std::string ProjectFileExtension;
+extern const std::string LegacyProjectFileExtension;
 extern const std::string LegacySchematicFileExtension;
 extern const std::string KiCadSchematicFileExtension;
 extern const std::string NetlistFileExtension;
diff --git a/kicad/import_project.cpp b/kicad/import_project.cpp
index 838081c43c..4d75fe595f 100644
--- a/kicad/import_project.cpp
+++ b/kicad/import_project.cpp
@@ -77,7 +77,7 @@ void KICAD_MANAGER_FRAME::OnImportEagleFiles( wxCommandEvent& event )
 
     wxFileName pro = sch;
 
-    pro.SetExt( ProjectFileExtension );
+    pro.SetExt( LegacyProjectFileExtension );
 
     wxString protitle = _( "KiCad Project Destination" );
 
@@ -115,7 +115,7 @@ void KICAD_MANAGER_FRAME::OnImportEagleFiles( wxCommandEvent& event )
     }
 
     wxFileName pcb( sch );
-    pro.SetExt( ProjectFileExtension );         // enforce extension
+    pro.SetExt( LegacyProjectFileExtension );         // enforce extension
     pcb.SetExt( LegacyPcbFileExtension );       // enforce extension
 
     if( !pro.IsAbsolute() )
diff --git a/kicad/tools/kicad_manager_control.cpp b/kicad/tools/kicad_manager_control.cpp
index 284f407dd5..4b4113ab2b 100644
--- a/kicad/tools/kicad_manager_control.cpp
+++ b/kicad/tools/kicad_manager_control.cpp
@@ -95,10 +95,10 @@ int KICAD_MANAGER_CONTROL::NewProject( const TOOL_EVENT& aEvent )
     // wxFileName automatically extracts an extension.  But if it isn't
     // a .pro extension, we should keep it as part of the filename
     if( !pro.GetExt().IsEmpty()
-        && pro.GetExt().ToStdString() != ProjectFileExtension )
+        && pro.GetExt().ToStdString() != LegacyProjectFileExtension )
         pro.SetName( pro.GetName() + wxT( "." ) + pro.GetExt() );
 
-    pro.SetExt( ProjectFileExtension );     // enforce extension
+    pro.SetExt( LegacyProjectFileExtension );     // enforce extension
 
     if( !pro.IsAbsolute() )
         pro.MakeAbsolute();
@@ -193,10 +193,10 @@ int KICAD_MANAGER_CONTROL::NewFromTemplate( const TOOL_EVENT& aEvent )
     // wxFileName automatically extracts an extension.  But if it isn't
     // a .pro extension, we should keep it as part of the filename
     if( !fn.GetExt().IsEmpty()
-        && fn.GetExt().ToStdString() != ProjectFileExtension )
+        && fn.GetExt().ToStdString() != LegacyProjectFileExtension )
         fn.SetName( fn.GetName() + wxT( "." ) + fn.GetExt() );
 
-    fn.SetExt( ProjectFileExtension );     // enforce extension
+    fn.SetExt( LegacyProjectFileExtension );     // enforce extension
 
     if( !fn.IsAbsolute() )
         fn.MakeAbsolute();
@@ -300,7 +300,7 @@ int KICAD_MANAGER_CONTROL::OpenProject( const TOOL_EVENT& aEvent )
         return -1;
 
     wxFileName pro( dlg.GetPath() );
-    pro.SetExt( ProjectFileExtension );     // enforce extension
+    pro.SetExt( LegacyProjectFileExtension );     // enforce extension
 
     if( !pro.IsAbsolute() )
         pro.MakeAbsolute();
diff --git a/kicad/tree_project_frame.cpp b/kicad/tree_project_frame.cpp
index d32aad898a..1856536648 100644
--- a/kicad/tree_project_frame.cpp
+++ b/kicad/tree_project_frame.cpp
@@ -509,7 +509,7 @@ void TREE_PROJECT_FRAME::ReCreateTreePrj()
         fn.Clear();
         fn.SetPath( wxStandardPaths::Get().GetDocumentsDir() );
         fn.SetName( NAMELESS_PROJECT );
-        fn.SetExt( ProjectFileExtension );
+        fn.SetExt( LegacyProjectFileExtension );
     }
 
     bool prjOpened = fn.FileExists();
diff --git a/pcbnew/dialogs/dialog_import_settings.cpp b/pcbnew/dialogs/dialog_import_settings.cpp
index 4b3c777b2c..6d7ec1a274 100644
--- a/pcbnew/dialogs/dialog_import_settings.cpp
+++ b/pcbnew/dialogs/dialog_import_settings.cpp
@@ -56,7 +56,7 @@ bool DIALOG_IMPORT_SETTINGS::TransferDataToWindow()
 void DIALOG_IMPORT_SETTINGS::OnBrowseClicked( wxCommandEvent& event )
 {
     wxFileName fn = m_frame->GetBoard()->GetFileName();
-    fn.SetExt( ProjectFileExtension );
+    fn.SetExt( LegacyProjectFileExtension );
 
     wxFileDialog dlg( this, _( "Import Settings From" ), fn.GetPath(), fn.GetFullName(),
                       ProjectFileWildcard(), wxFD_OPEN | wxFD_FILE_MUST_EXIST | wxFD_CHANGE_DIR );
diff --git a/pcbnew/files.cpp b/pcbnew/files.cpp
index f33cc9b109..08b800e2d1 100644
--- a/pcbnew/files.cpp
+++ b/pcbnew/files.cpp
@@ -308,7 +308,7 @@ bool PCB_EDIT_FRAME::Files_io_from_id( int id )
             return false;
 
         wxFileName fn( wxStandardPaths::Get().GetDocumentsDir(), wxT( "noname" ),
-                       ProjectFileExtension );
+                       LegacyProjectFileExtension );
 
         Prj().SetProjectFullName( fn.GetFullPath() );
 
@@ -477,7 +477,7 @@ bool PCB_EDIT_FRAME::OpenProjectFiles( const std::vector<wxString>& aFileSet, in
     ReleaseFile();
 
     wxFileName pro = fullFileName;
-    pro.SetExt( ProjectFileExtension );
+    pro.SetExt( LegacyProjectFileExtension );
 
     bool is_new = !wxFileName::IsFileReadable( fullFileName );
 
diff --git a/qa/eeschema/test_netlists.cpp b/qa/eeschema/test_netlists.cpp
index 655381a60b..2cad8aa444 100644
--- a/qa/eeschema/test_netlists.cpp
+++ b/qa/eeschema/test_netlists.cpp
@@ -81,7 +81,7 @@ void TEST_NETLISTS_FIXTURE::loadSchematic( const wxString& aBaseName )
     BOOST_TEST_MESSAGE( fn );
 
     wxFileName pro( fn );
-    pro.SetExt( ProjectFileExtension );
+    pro.SetExt( LegacyProjectFileExtension );
 
     m_project.SetProjectFullName( pro.GetFullPath() );
     m_project.SetElem( PROJECT::ELEM_SCH_PART_LIBS, nullptr );