diff --git a/ReactCommon/react/renderer/mapbuffer/MapBufferBuilder.cpp b/ReactCommon/react/renderer/mapbuffer/MapBufferBuilder.cpp
index 54a7fa03bf8f3b..d2b37e2ff41f9f 100644
--- a/ReactCommon/react/renderer/mapbuffer/MapBufferBuilder.cpp
+++ b/ReactCommon/react/renderer/mapbuffer/MapBufferBuilder.cpp
@@ -127,7 +127,7 @@ void MapBufferBuilder::ensureDynamicDataSpace(int32_t size) {
 }
 
 void MapBufferBuilder::putString(Key key, std::string value) {
-  int32_t strLength = value.length();
+  int32_t strLength = static_cast<int32_t>(value.length());
   const char *cstring = getCstring(&value);
 
   // format [lenght of string (int)] + [Array of Characters in the string]
@@ -223,4 +223,4 @@ MapBufferBuilder::~MapBufferBuilder() {
 }
 
 } // namespace react
-} // namespace facebook
+} // namespace facebook
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