--- a/js/src/jit/x64/CodeGenerator-x64.cpp
+++ b/js/src/jit/x64/CodeGenerator-x64.cpp
@@ -373,17 +373,17 @@ CodeGeneratorX64::visitMulI64(LMulI64* l
             return;
           case 2:
             masm.addq(lhs, lhs);
             return;
           default:
             if (constant > 0) {
                 // Use shift if constant is power of 2.
                 int32_t shift = mozilla::FloorLog2(constant);
-                if (int64_t(1 << shift) == constant) {
+                if (int64_t(1) << shift == constant) {
                     masm.shlq(Imm32(shift), lhs);
                     return;
                 }
             }
             masm.mul64(Imm64(constant), Register64(lhs));
         }
     } else {
         masm.imulq(ToOperand(rhs), lhs);