Fix typo.
diff --git a/Modules/structmodule.c b/Modules/structmodule.c
index 86ac366..df80302 100644
--- a/Modules/structmodule.c
+++ b/Modules/structmodule.c
@@ -1515,5 +1515,5 @@
 			return;
 	}
 	Py_INCREF(StructError);
-	PyModule_AddObject(d, "error", StructError);
+	PyModule_AddObject(m, "error", StructError);
 }