diff --git a/src/hb-font.cc b/src/hb-font.cc
index 223b2b4f3..ba8ab0dcc 100644
--- a/src/hb-font.cc
+++ b/src/hb-font.cc
@@ -144,7 +144,7 @@ hb_font_funcs_make_immutable (hb_font_funcs_t *ffuncs)
 hb_bool_t
 hb_font_funcs_is_immutable (hb_font_funcs_t *ffuncs)
 {
-  return ffuncs->immutable = TRUE;
+  return ffuncs->immutable;
 }