diff --git a/third_party/skia/src/ports/SkTypeface_mac_ct.cpp b/third_party/skia/src/ports/SkTypeface_mac_ct.cpp
index 0000000000..1111111111 100644
--- a/third_party/skia/src/ports/SkTypeface_mac_ct.cpp
+++ b/third_party/skia/src/ports/SkTypeface_mac_ct.cpp
@@ -383,7 +383,9 @@ static void populate_glyph_to_unicode_slow(CTFontRef ctFont, CFIndex glyphCount,
     while (glyphCount > 0) {
         CGGlyph glyph;
         if (CTFontGetGlyphsForCharacters(ctFont, &unichar, &glyph, 1)) {
-            if (out[glyph] == 0) {
+            // CoreText may return a glyph id >= glyphCount for fonts whose
+            // cmap disagrees with maxp.numGlyphs. Match get_plane_glyph_map.
+            if (glyph < glyphCount && out[glyph] == 0) {
                 out[glyph] = unichar;
                 --glyphCount;
             }