diff --git a/src/mesa/shader/arbprogparse.c b/src/mesa/shader/arbprogparse.c
index e7875242821..4de8ccf0873 100644
--- a/src/mesa/shader/arbprogparse.c
+++ b/src/mesa/shader/arbprogparse.c
@@ -3916,7 +3916,7 @@ _mesa_parse_arb_vertex_program(GLcontext *ctx, GLenum target,
    ASSERT(target == GL_VERTEX_PROGRAM_ARB);
 
    if (!_mesa_parse_arb_program(ctx, target, (const GLubyte*) str, len, &ap)) {
-      /* Error in the program. Just return. */
+      _mesa_error(ctx, GL_INVALID_OPERATION, "glProgramString(bad program)");
       return;
    }