--- core/fxge/cfx_glyphcache.cpp
+++ core/fxge/cfx_glyphcache.cpp
@@ -183,7 +183,8 @@ std::unique_ptr<CFX_GlyphBitmap> CFX_GlyphCache::RenderGlyph(
       }
     }
   } else {
-    memset(pDestBuf, 0, dest_pitch * bmheight);
+    if (dest_pitch != 0 && bmheight != 0)
+      memset(pDestBuf, 0, dest_pitch * bmheight);
     int rowbytes = std::min(abs(src_pitch), dest_pitch);
     for (int row = 0; row < bmheight; row++)
       memcpy(pDestBuf + row * dest_pitch, pSrcBuf + row * src_pitch, rowbytes);