diff --git a/gtk/gtktextiter.c b/gtk/gtktextiter.c
index 51c8f8f0320c66e1ec03223c90cf0133b39394c9..c399f6fe8b184509a7ce2e36df886614138d557a 100644
--- a/gtk/gtktextiter.c
+++ b/gtk/gtktextiter.c
@@ -4476,7 +4476,7 @@ exact_prefix_cmp (const gchar *string,
   /* If string contains prefix, check that prefix is not followed
    * by a unicode mark symbol, e.g. that trailing 'a' in prefix
    * is not part of two-char a-with-hat symbol in string. */
-  return type != G_UNICODE_COMBINING_MARK &&
+  return type != G_UNICODE_SPACING_MARK &&
          type != G_UNICODE_ENCLOSING_MARK &&
          type != G_UNICODE_NON_SPACING_MARK;
 }