diff --git a/hphp/compiler/expression/binary_op_expression.cpp b/hphp/compiler/expression/binary_op_expression.cpp
index 4685bd7c1669e..93abadfdce95d 100644
--- a/hphp/compiler/expression/binary_op_expression.cpp
+++ b/hphp/compiler/expression/binary_op_expression.cpp
@@ -374,14 +374,16 @@ ExpressionPtr BinaryOpExpression::foldConst(AnalysisResultConstRawPtr ar) {
         case T_SL: {
           int64_t shift = v2.toInt64();
           if (!RuntimeOption::PHP7_IntSemantics) {
-            result = v1.toInt64() << (shift & 63);
+            result = static_cast<int64_t>(
+              static_cast<uint64_t>(v1.toInt64()) << (shift & 63));
           } else if (shift >= 64) {
             result = 0;
           } else if (shift < 0) {
             // This raises an error, and so can't be folded.
             return ExpressionPtr();
           } else {
-            result = v1.toInt64() << (shift & 63);
+            result = static_cast<int64_t>(
+              static_cast<uint64_t>(v1.toInt64()) << (shift & 63));
           }
           break;
         }