diff --git a/src/mesa/main/genmipmap.c b/src/mesa/main/genmipmap.c
index 1a6ae9a5f3c..d917220f7e8 100644
--- a/src/mesa/main/genmipmap.c
+++ b/src/mesa/main/genmipmap.c
@@ -139,7 +139,8 @@ _mesa_generate_texture_mipmap(struct gl_context *ctx,
                                                               srcImage->InternalFormat)) {
       _mesa_unlock_texture(ctx, texObj);
       _mesa_error(ctx, GL_INVALID_OPERATION,
-                  "glGenerate%sMipmap(invalid internal format)", suffix);
+                  "glGenerate%sMipmap(invalid internal format %s)", suffix,
+                  _mesa_enum_to_string(srcImage->InternalFormat));
       return;
    }