diff --git a/Source/cmVTKWrapTclCommand.cxx b/Source/cmVTKWrapTclCommand.cxx
index 9c808b0e7..03e213ac0 100644
--- a/Source/cmVTKWrapTclCommand.cxx
+++ b/Source/cmVTKWrapTclCommand.cxx
@@ -237,7 +237,10 @@ bool cmVTKWrapTclCommand::WriteInit(const char *kitName,
   
   if (!strcmp(kitName,"Vtkcommontcl"))
     {
-    fprintf(fout,"int vtkCommand(ClientData cd, Tcl_Interp *interp,\n             int argc, char *argv[]);\n");
+    fprintf(fout,"extern \"C\" {\n"
+                 "  int vtkCommand(ClientData cd, Tcl_Interp *interp,\n"
+                 "                 int argc, char *argv[]);\n"
+                 "}\n");
     fprintf(fout,"\nTcl_HashTable vtkInstanceLookup;\n");
     fprintf(fout,"Tcl_HashTable vtkPointerLookup;\n");
     fprintf(fout,"Tcl_HashTable vtkCommandLookup;\n");