--- a/gfx/thebes/gfxFont.h
+++ b/gfx/thebes/gfxFont.h
@@ -1298,16 +1298,21 @@ private:
         }
 
         nsTArray<uintptr_t> mBlocks;
     };
 
     GlyphWidths             mContainedGlyphWidths;
     nsTHashtable<HashEntry> mTightGlyphExtents;
     int32_t                 mAppUnitsPerDevUnit;
+
+private:
+    // not implemented:
+    gfxGlyphExtents(const gfxGlyphExtents& aOther) MOZ_DELETE;
+    gfxGlyphExtents& operator=(const gfxGlyphExtents& aOther) MOZ_DELETE;
 };
 
 /**
  * gfxFontShaper
  *
  * This class implements text shaping (character to glyph mapping and
  * glyph layout). There is a gfxFontShaper subclass for each text layout
  * technology (uniscribe, core text, harfbuzz,....) we support.