diff --git a/src/hydrogen-instructions.cc b/src/hydrogen-instructions.cc
index 29d4e73cba..a35134952d 100644
--- a/src/hydrogen-instructions.cc
+++ b/src/hydrogen-instructions.cc
@@ -3955,7 +3955,7 @@ HInstruction* HUnaryMathOperation::New(
       case kMathFloor:
         return H_CONSTANT_DOUBLE(std::floor(d));
       case kMathClz32: {
-        uint32_t i = static_cast<uint32_t>(constant->Integer32Value());
+        uint32_t i = DoubleToUint32(d);
         return H_CONSTANT_INT(
             (i == 0) ? 32 : CompilerIntrinsics::CountLeadingZeros(i));
       }
diff --git a/test/mjsunit/regress/regress-347906.js b/test/mjsunit/regress/regress-347906.js
new file mode 100644
index 0000000000..c751618928
--- /dev/null
+++ b/test/mjsunit/regress/regress-347906.js
@@ -0,0 +1,14 @@
+// Copyright 2014 the V8 project authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+// Flags: --allow-natives-syntax --harmony
+
+function foo() {
+  return Math.clz32(12.34);
+}
+
+foo();
+foo();
+%OptimizeFunctionOnNextCall(foo);
+foo();