diff --git a/lib/scripts/convertDefault.py b/lib/scripts/convertDefault.py
index 63d0e09c6a..40bc8b53c8 100644
--- a/lib/scripts/convertDefault.py
+++ b/lib/scripts/convertDefault.py
@@ -15,7 +15,7 @@
 # The user can also redefine this default converter, placing their
 # replacement in ~/.lyx/scripts
 
-# converts an image from $1 to $2 format
+# converts an image $2 (format $1) to $4 (format $3)
 import os, re, sys
 
 # We may need some extra options only supported by recent convert versions
@@ -42,15 +42,15 @@ else:
 
 opts = "-depth 8"
 
-# If supported, add the -define option for pdf source formats 
-if sys.argv[1][:4] == 'pdf:' and (version >= 0x060206 or gm):
+# If supported, add the -define option for pdf source formats
+if sys.argv[1] == 'pdf' and (version >= 0x060206 or gm):
     opts = '-define pdf:use-cropbox=true ' + opts
 
 # If supported, add the -flatten option for ppm target formats (see bug 4749)
-if sys.argv[2][:4] == 'ppm:' and (version >= 0x060305 or gm):
+if sys.argv[3] == 'ppm' and (version >= 0x060305 or gm):
     opts = opts + ' -flatten'
 
-if os.system(r'convert %s "%s" "%s"' % (opts, sys.argv[1], sys.argv[2])) != 0:
+if os.system(r'convert %s "%s" "%s"' % (opts, sys.argv[2], sys.argv[3] + ':' + sys.argv[4])) != 0:
     print >> sys.stderr, sys.argv[0], 'ERROR'
     print >> sys.stderr, 'Execution of "convert" failed.'
     sys.exit(1)
diff --git a/src/Converter.cpp b/src/Converter.cpp
index 933e2f673b..0f97b7396e 100644
--- a/src/Converter.cpp
+++ b/src/Converter.cpp
@@ -299,10 +299,10 @@ bool Converters::convert(Buffer const * buffer,
 			string const command =
 				os::python() + ' ' +
 				quoteName(libFileSearch("scripts", "convertDefault.py").toFilesystemEncoding()) +
-				' ' +
-				quoteName(from_ext + ':' + from_file.toFilesystemEncoding()) +
-				' ' +
-				quoteName(to_ext + ':' + to_file.toFilesystemEncoding());
+				' ' + from_ext + ' ' +
+				quoteName(from_file.toFilesystemEncoding()) +
+				' ' + to_ext + ' ' +
+				quoteName(to_file.toFilesystemEncoding());
 			LYXERR(Debug::FILES, "No converter defined! "
 				   "I use convertDefault.py:\n\t" << command);
 			Systemcall one;
diff --git a/src/graphics/GraphicsConverter.cpp b/src/graphics/GraphicsConverter.cpp
index 3201d5d06a..4bd5cf1ef4 100644
--- a/src/graphics/GraphicsConverter.cpp
+++ b/src/graphics/GraphicsConverter.cpp
@@ -324,13 +324,15 @@ static void build_script(string const & from_file,
 		ostringstream os;
 		os << os::python() << ' '
 		   << commandPrep("$$s/scripts/convertDefault.py") << ' ';
-		if (!from_format.empty())
-			os << strip_digit(from_format) << ':';
+		if (from_format.empty())
+			os << "unknown ";
+		else
+			os << strip_digit(from_format) << ' ';
 		// The extra " quotes around infile and outfile are needed
 		// because the filename may contain spaces and it is used
 		// as argument of os.system().
 		os << "' + '\"' + infile + '\"' + ' "
-		   << strip_digit(to_format) << ":' + '\"' + outfile + '\"' + '";
+		   << strip_digit(to_format) << " ' + '\"' + outfile + '\"' + '";
 		string const command = os.str();
 
 		LYXERR(Debug::GRAPHICS,