diff --git a/src/opst.cpp b/src/opst.cpp
index c3ec669..d693652 100644
--- a/src/opst.cpp
+++ b/src/opst.cpp
@@ -84,15 +84,12 @@ void pwmInFallingEdgeISR()
 {
     mOpstFiFo.mData[mOpstFiFo.mIn].mFalling = micros();
     mOpstFiFo.mIn++;
+    mOpstFiFo.mIn %= OPST_FIFO_SIZE;
 
     if(mOpstFiFo.mOut == mOpstFiFo.mIn)
     {
         mOpstFiFo.mOverrun = true;
     }
-    if(OPST_FIFO_SIZE <= mOpstFiFo.mIn)
-    {
-        mOpstFiFo.mIn = 0;
-    }
     attachInterrupt(digitalPinToInterrupt(mOpstPin), pwmInRisingEdgeISR, RISING);
 }
 
@@ -131,14 +128,8 @@ void opstUpdate()
             uint32_t pulseInterval = 0; // time between rising edge of current pulse and rising edge of following pulse
             uint32_t pulseLen = 0; // time between rising edge of current pulse and falling edge of current pulse
 
-            if(OPST_FIFO_SIZE > (mOpstFiFo.mOut + 1))
-            {
-                nextOut = mOpstFiFo.mOut + 1;
-            }
-            else
-            {
-                nextOut = 0;
-            }
+            nextOut = mOpstFiFo.mOut + 1;
+            nextOut %= OPST_FIFO_SIZE;
 
             pulseInterval = mOpstFiFo.mData[nextOut].mRising - mOpstFiFo.mData[mOpstFiFo.mOut].mRising;
             pulseLen = mOpstFiFo.mData[mOpstFiFo.mOut].mFalling - mOpstFiFo.mData[mOpstFiFo.mOut].mRising;