diff --git a/deps/icu-small/source/common/unistr.cpp b/deps/icu-small/source/common/unistr.cpp
index eeb0c3a..1c59de9 100644
--- a/deps/icu-small/source/common/unistr.cpp
+++ b/deps/icu-small/source/common/unistr.cpp
@@ -1563,7 +1563,11 @@ UnicodeString::doAppend(const UChar *srcChars, int32_t srcStart, int32_t srcLeng
   }

   int32_t oldLength = length();
-  int32_t newLength = oldLength + srcLength;
+  int32_t newLength;
+  if (uprv_add32_overflow(oldLength, srcLength, &newLength)) {
+    setToBogus();
+    return *this;
+  }

   // Check for append onto ourself
   const UChar* oldArray = getArrayStart();