diff --git a/gobject/gtype.h b/gobject/gtype.h
index 7c3936b48..b564bbb96 100644
--- a/gobject/gtype.h
+++ b/gobject/gtype.h
@@ -1949,7 +1949,7 @@ _G_DEFINE_TYPE_EXTENDED_CLASS_INIT(TypeName, type_name) \
 \
 G_GNUC_UNUSED \
 static inline gpointer \
-type_name##_get_instance_private (const TypeName *self) \
+type_name##_get_instance_private (TypeName *self) \
 { \
   return (G_STRUCT_MEMBER_P (self, TypeName##_private_offset)); \
 } \