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();