diff --git a/glib/gstring.h b/glib/gstring.h
index 17a7e3c2d..8e4cc5657 100644
--- a/glib/gstring.h
+++ b/glib/gstring.h
@@ -168,7 +168,7 @@ static inline GString*
 g_string_append_c_inline (GString *gstring,
                           gchar    c)
 {
-  if (gstring->len + 1 < gstring->allocated_len)
+  if (G_LIKELY (gstring->len + 1 < gstring->allocated_len))
     {
       gstring->str[gstring->len++] = c;
       gstring->str[gstring->len] = 0;