diff --git a/src/google/protobuf/stubs/strutil.cc b/src/google/protobuf/stubs/strutil.cc
index 3844fa6b8b6..5486887295f 100644
--- a/src/google/protobuf/stubs/strutil.cc
+++ b/src/google/protobuf/stubs/strutil.cc
@@ -1065,10 +1065,12 @@ char* FastUInt32ToBufferLeft(uint32 u, char* buffer) {
 }
 
 char* FastInt32ToBufferLeft(int32 i, char* buffer) {
-  uint32 u = i;
+  uint32 u = 0;
   if (i < 0) {
     *buffer++ = '-';
-    u = -i;
+    u -= i;
+  } else {
+    u = i;
   }
   return FastUInt32ToBufferLeft(u, buffer);
 }