diff --git a/src/core/SkGlyph.cpp b/src/core/SkGlyph.cpp
index 4b81077..30a7ea1 100644
--- a/src/core/SkGlyph.cpp
+++ b/src/core/SkGlyph.cpp
@@ -284,7 +284,10 @@
     buffer.writeUInt(fID.value());
     buffer.writePoint({fAdvanceX, fAdvanceY});
     buffer.writeUInt(fWidth << 16 | fHeight);
-    buffer.writeUInt(fLeft << 16 | fTop);
+    // Note: << has undefined behavior for negative values.
+    const uint32_t left = fLeft;
+    const uint32_t top = fTop;
+    buffer.writeUInt(left << 16 | top);
     buffer.writeUInt(SkTo<uint32_t>(fMaskFormat));
 }