diff --git a/include/board_design_settings.h b/include/board_design_settings.h
index 171775db06..8ca74f6d72 100644
--- a/include/board_design_settings.h
+++ b/include/board_design_settings.h
@@ -304,12 +304,12 @@ public:
     /**
      * @return the biggest clearance value found in NetClasses list.
      */
-    int GetBiggestClearanceValue();
+    int GetBiggestClearanceValue() const;
 
     /**
      * @return the smallest clearance value found in NetClasses list.
      */
-    int GetSmallestClearanceValue();
+    int GetSmallestClearanceValue() const;
 
     /**
      * @return the current micro via size that is the current netclass value.
@@ -547,8 +547,10 @@ public:
     {
         if( m_useCustomDiffPair )
             return m_customDiffPair.m_Width;
-        else
+        else if( m_diffPairIndex < m_DiffPairDimensionsList.size() )
             return m_DiffPairDimensionsList[m_diffPairIndex].m_Width;
+        else
+            return GetCurrentTrackWidth();
     }
 
     /**
@@ -560,8 +562,10 @@ public:
     {
         if( m_useCustomDiffPair )
             return m_customDiffPair.m_Gap;
-        else
+        else if( m_diffPairIndex < m_DiffPairDimensionsList.size() )
             return m_DiffPairDimensionsList[m_diffPairIndex].m_Gap;
+        else
+            return GetSmallestClearanceValue();
     }
 
     /**
@@ -573,8 +577,10 @@ public:
     {
         if( m_useCustomDiffPair )
             return m_customDiffPair.m_ViaGap;
-        else
+        else if( m_diffPairIndex < m_DiffPairDimensionsList.size() )
             return m_DiffPairDimensionsList[m_diffPairIndex].m_ViaGap;
+        else
+            return GetSmallestClearanceValue();
     }
 
     /**
diff --git a/pcbnew/board_design_settings.cpp b/pcbnew/board_design_settings.cpp
index 907c90ff99..2265db8fab 100644
--- a/pcbnew/board_design_settings.cpp
+++ b/pcbnew/board_design_settings.cpp
@@ -868,7 +868,7 @@ bool BOARD_DESIGN_SETTINGS::Ignore( int aDRCErrorCode )
 }
 
 
-int BOARD_DESIGN_SETTINGS::GetBiggestClearanceValue()
+int BOARD_DESIGN_SETTINGS::GetBiggestClearanceValue() const
 {
     int            biggest = 0;
     DRC_CONSTRAINT constraint;
@@ -889,7 +889,7 @@ int BOARD_DESIGN_SETTINGS::GetBiggestClearanceValue()
 }
 
 
-int BOARD_DESIGN_SETTINGS::GetSmallestClearanceValue()
+int BOARD_DESIGN_SETTINGS::GetSmallestClearanceValue() const
 {
     int clearance = GetDefault()->GetClearance();