diff --git a/dom/vr/VRDisplay.cpp b/dom/vr/VRDisplay.cpp
index 89b262fedd1d..8ca52d4ce412 100644
--- a/dom/vr/VRDisplay.cpp
+++ b/dom/vr/VRDisplay.cpp
@@ -743,7 +743,7 @@ void VRFrameInfo::Update(const gfx::VRDisplayInfo& aInfo,
      * has a base of 0, which is not necessarily true in all UA's.
      */
     mTimeStampOffset =
-        float(rand()) / RAND_MAX * 10000.0f + 1000.0f - aState.timestamp;
+        float(rand()) / float(RAND_MAX) * 10000.0f + 1000.0f - aState.timestamp;
   }
   mVRState.timestamp = aState.timestamp + mTimeStampOffset;