diff --git a/utils/fgpanel/FGPanelApplication.cxx b/utils/fgpanel/FGPanelApplication.cxx
index 0477be7e2..b58700477 100644
--- a/utils/fgpanel/FGPanelApplication.cxx
+++ b/utils/fgpanel/FGPanelApplication.cxx
@@ -103,7 +103,7 @@ FGPanelApplication::FGPanelApplication( int argc, char ** argv ) :
     string arg = argv[i];
     if( arg.find( "--prop:" ) == 0 ) {
       string s2 = arg.substr( 7 );
-      unsigned p = s2.find( "=" );
+      string::size_type p = s2.find( "=" );
       if( p != string::npos ) {
         string propertyName = s2.substr( 0, p );
         string propertyValue = s2.substr( p+1 );