diff --git a/content/media/webaudio/OscillatorNode.cpp b/content/media/webaudio/OscillatorNode.cpp
index adf3292c8b1b..9444c66b9426 100644
--- a/content/media/webaudio/OscillatorNode.cpp
+++ b/content/media/webaudio/OscillatorNode.cpp
@@ -376,16 +376,18 @@ public:
     float* higherWaveData = nullptr;
     float* lowerWaveData = nullptr;
     float tableInterpolationFactor;
-    float rate = 1.0 / mSource->SampleRate();
- 
+    // Phase increment at frequency of 1 Hz.
+    // mPhase runs [0,periodicWaveSize) here instead of [0,2*M_PI).
+    float basePhaseIncrement =
+      static_cast<float>(periodicWaveSize) / mSource->SampleRate();
+
     for (uint32_t i = aStart; i < aEnd; ++i) {
       UpdateParametersIfNeeded(ticks, i);
       mPeriodicWave->waveDataForFundamentalFrequency(mFinalFrequency,
                                                      lowerWaveData,
                                                      higherWaveData,
                                                      tableInterpolationFactor);
-      // mPhase runs 0..periodicWaveSize here instead of 0..2*M_PI.
-      mPhase += periodicWaveSize * mFinalFrequency * rate;
+      mPhase += basePhaseIncrement * mFinalFrequency;
       mPhase = fmod(mPhase, periodicWaveSize);
       // Bilinear interpolation between adjacent samples in each table.
       uint32_t j1 = floor(mPhase);