diff --git a/src/hb-glib.cc b/src/hb-glib.cc
index 1b322ea50..1fd54e5d2 100644
--- a/src/hb-glib.cc
+++ b/src/hb-glib.cc
@@ -254,8 +254,10 @@ hb_glib_unicode_compose (hb_unicode_funcs_t *ufuncs HB_UNUSED,
   len = g_unichar_to_utf8 (a, utf8);
   len += g_unichar_to_utf8 (b, utf8 + len);
   normalized = g_utf8_normalize (utf8, len, G_NORMALIZE_NFC);
-
   len = g_utf8_strlen (normalized, -1);
+  if (unlikely (!len))
+    return FALSE;
+
   if (len == 1) {
     *ab = g_utf8_get_char (normalized);
     ret = TRUE;
@@ -288,8 +290,10 @@ hb_glib_unicode_decompose (hb_unicode_funcs_t *ufuncs HB_UNUSED,
 
   len = g_unichar_to_utf8 (ab, utf8);
   normalized = g_utf8_normalize (utf8, len, G_NORMALIZE_NFD);
-
   len = g_utf8_strlen (normalized, -1);
+  if (unlikely (!len))
+    return FALSE;
+
   if (len == 1) {
     *a = g_utf8_get_char (normalized);
     *b = 0;