diff --git a/glib/gtestutils.c b/glib/gtestutils.c
index a21c3e568..db2be7b98 100644
--- a/glib/gtestutils.c
+++ b/glib/gtestutils.c
@@ -1390,7 +1390,7 @@ g_assertion_message_error (const char     *domain,
 			   int             line,
 			   const char     *func,
 			   const char     *expr,
-			   GError         *error,
+			   const GError   *error,
 			   GQuark          error_domain,
 			   int             error_code)
 {
diff --git a/glib/gtestutils.h b/glib/gtestutils.h
index fdcc24a21..bfdf8cc8e 100644
--- a/glib/gtestutils.h
+++ b/glib/gtestutils.h
@@ -211,7 +211,7 @@ void    g_assertion_message_error       (const char     *domain,
                                          int             line,
                                          const char     *func,
                                          const char     *expr,
-                                         GError         *error,
+                                         const GError   *error,
                                          GQuark          error_domain,
                                          int             error_code) G_GNUC_NORETURN;
 void    g_test_add_vtable               (const char     *testpath,