diff --git a/common/dsnlexer.cpp b/common/dsnlexer.cpp
index 6f8f6d064c..883a85db38 100644
--- a/common/dsnlexer.cpp
+++ b/common/dsnlexer.cpp
@@ -369,18 +369,25 @@ int DSNLEXER::NeedNUMBER( const char* aExpectation ) throw( IO_ERROR )
 
 /**
  * Function isSpace
- * strips the upper bits of the int to ensure the value passed to C++ %isspace() is
- * in the range of 0-255
+ * tests for whitespace.  Our whitespace, by our definition, is a subset of ASCII,
+ * i.e. no bytes with MSB on can be considered whitespace, since they are likely part
+ * of a multibyte UTF8 character.
  */
-static inline bool isSpace( int cc )
+static bool isSpace( int cc )
 {
-    // Warning: we are using UTF8 char, so values are coded from 0x01 to 0xFF
-    // isspace( int value ) works fine under Linux,
-    // but seems use only a 7 bits value under mingw, in comparisons.
-    // (for instance 0xA0 is seen as 0x20)
-    // So we need to test if the value is ASCII ( <= 127) and a space ( ' ', \t, \n ... )
-    // and not just a space:
-    return  ( (unsigned) cc <= 127 ) && ::isspace( cc );
+    if( cc <= ' ' )
+    {
+        switch( cc )
+        {
+        case ' ':
+        case '\n':
+        case '\r':
+        case '\t':
+        case '\0':              // PCAD s-expression files have this.
+            return true;
+        }
+    }
+    return false;
 }
 
 
diff --git a/common/richio.cpp b/common/richio.cpp
index 0b3a1f8ef8..4ab811d96c 100644
--- a/common/richio.cpp
+++ b/common/richio.cpp
@@ -90,6 +90,11 @@ FILE_LINE_READER::FILE_LINE_READER( FILE* aFile, const wxString& aFileName,
     iOwn( doOwn ),
     fp( aFile )
 {
+    if( doOwn )
+    {
+        setvbuf( fp, NULL, _IOFBF, BUFSIZ * 8 );
+    }
+
     source  = aFileName;
     lineNum = aStartingLineNumber;
 }
@@ -101,6 +106,10 @@ FILE_LINE_READER::~FILE_LINE_READER()
         fclose( fp );
 }
 
+#if 0
+
+// The strlen() will trip on embedded nuls which can come in via bad data files.
+// Try an alternate technique below.
 
 unsigned FILE_LINE_READER::ReadLine() throw( IO_ERROR )
 {
@@ -129,6 +138,40 @@ unsigned FILE_LINE_READER::ReadLine() throw( IO_ERROR )
     return length;
 }
 
+#else
+unsigned FILE_LINE_READER::ReadLine() throw( IO_ERROR )
+{
+    length = 0;
+
+    for(;;)
+    {
+        if( length >= maxLineLength )
+            THROW_IO_ERROR( _( "Maximum line length exceeded" ) );
+
+        if( length >= capacity )
+            expandCapacity( capacity * 2 );
+
+        // faster, POSIX compatible fgetc(), no locking.
+        int cc = getc_unlocked( fp );
+        if( cc == EOF )
+            break;
+
+        line[ length++ ] = (char) cc;
+
+        if( cc == '\n' )
+            break;
+    }
+
+    line[ length ] = 0;
+
+    // lineNum is incremented even if there was no line read, because this
+    // leads to better error reporting when we hit an end of file.
+    ++lineNum;
+
+    return length;
+}
+#endif
+
 
 STRING_LINE_READER::STRING_LINE_READER( const std::string& aString, const wxString& aSource ) :
     LINE_READER( LINE_READER_LINE_DEFAULT_MAX ),