diff --git a/src/emucore/tia/TIA.cxx b/src/emucore/tia/TIA.cxx
index 98ed5ffa3..e11d73190 100644
--- a/src/emucore/tia/TIA.cxx
+++ b/src/emucore/tia/TIA.cxx
@@ -583,7 +583,6 @@ bool TIA::poke(uInt16 address, uInt8 value)
       updateDumpPorts(value);
 
       myDelayQueue.push(VBLANK, value, Delay::vblank);
-
       break;
 
     case AUDV0:
@@ -1936,7 +1935,7 @@ void TIA::delayedWrite(uInt8 address, uInt8 value)
   {
     case VBLANK:
       flushLineCache();
-      myFrameManager->setVblank(value & 0x02);
+      myFrameManager->setVblank(value & 0x02, mySystem->cycles());
       break;
 
     case HMOVE:
diff --git a/src/emucore/tia/frame-manager/AbstractFrameManager.cxx b/src/emucore/tia/frame-manager/AbstractFrameManager.cxx
index 0f5d51ec6..cbb1d5cef 100644
--- a/src/emucore/tia/frame-manager/AbstractFrameManager.cxx
+++ b/src/emucore/tia/frame-manager/AbstractFrameManager.cxx
@@ -62,13 +62,13 @@ void AbstractFrameManager::clearHandlers()
 }
 
 // - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
-void AbstractFrameManager::setVblank(bool vblank)
+void AbstractFrameManager::setVblank(bool vblank, uInt64 cycles)
 {
   if (vblank == myVblank) return;
 
   myVblank = vblank;
 
-  onSetVblank();
+  onSetVblank(cycles);
 }
 
 // - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
diff --git a/src/emucore/tia/frame-manager/AbstractFrameManager.hxx b/src/emucore/tia/frame-manager/AbstractFrameManager.hxx
index 87a636146..4b892293c 100644
--- a/src/emucore/tia/frame-manager/AbstractFrameManager.hxx
+++ b/src/emucore/tia/frame-manager/AbstractFrameManager.hxx
@@ -63,7 +63,7 @@ class AbstractFrameManager : public Serializable
     /**
      * Called by TIA on VBLANK writes.
      */
-    void setVblank(bool vblank);
+    void setVblank(bool vblank, uInt64 cycles);
 
     /**
      * Called by TIA on VSYNC writes.
@@ -218,7 +218,7 @@ class AbstractFrameManager : public Serializable
     /**
      * Called if vblank changes.
      */
-    virtual void onSetVblank() {}
+    virtual void onSetVblank(uInt64 cycles) {}
 
     /**
      * Called if vsync changes.
diff --git a/src/emucore/tia/frame-manager/FrameManager.cxx b/src/emucore/tia/frame-manager/FrameManager.cxx
index 63667c073..8a304df1d 100644
--- a/src/emucore/tia/frame-manager/FrameManager.cxx
+++ b/src/emucore/tia/frame-manager/FrameManager.cxx
@@ -34,7 +34,7 @@ void FrameManager::onReset()
   myState = State::waitForVsyncStart;
   myLineInState = 0;
   myTotalFrames = 0;
-  myVsyncLines = 0;
+  myVsyncLineCount = 0;
   myY = 0;
 
   myJitterEmulation.reset();
@@ -50,14 +50,19 @@ void FrameManager::onNextLine()
   {
     case State::waitForVsyncStart:
       if ((myCurrentFrameTotalLines > myFrameLines - 3) || myTotalFrames == 0)
-        ++myVsyncLines;
+      {
+        if (myVblank)
+          ++myVsyncLineCount;
+      }
 
-      if (myVsyncLines > Metrics::maxLinesVsync) setState(State::waitForFrameStart);
+      if (myVsyncLineCount > Metrics::maxLinesVsync) setState(State::waitForFrameStart);
 
       break;
 
     case State::waitForVsyncEnd:
-      if (++myVsyncLines > Metrics::maxLinesVsync)
+      if (myVblank)
+        ++myVsyncLineCount;
+      if (myVsyncLineCount > Metrics::maxLinesVsync)
         setState(State::waitForFrameStart);
 
       break;
@@ -112,16 +117,38 @@ void FrameManager::setAdjustVSize(Int32 adjustVSize)
   recalculateMetrics();
 }
 
+// - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+void FrameManager::onSetVblank(uInt64 cycles)
+{
+  if (myState == State::waitForVsyncEnd)
+    if (myVblank) // VBLANK switched on
+    {
+      myVblankStart = cycles;
+      cerr << ", VBLANK ON " << cycles;
+    }
+    else // VBLANK switched off
+    {
+      myVblankCycles += cycles - myVblankStart;
+      cerr << ", VBLANK OFF " << cycles;
+    }
+}
+
 // - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
 void FrameManager::onSetVsync(uInt64 cycles)
 {
   if (myState == State::waitForVsyncEnd) {
     myVsyncEnd = cycles;
+    if(myVblankStart != INT64_MAX)
+      myVblankCycles += cycles - myVblankStart;
     setState(State::waitForFrameStart);
+    cerr << ", VSYNC waitForVsyncEnd " << cycles << " \n";
   }
   else {
     myVsyncStart = cycles;
+    myVblankStart = myVblank ? cycles : INT64_MAX;
+    myVblankCycles = 0;
     setState(State::waitForVsyncEnd);
+    cerr << ", VSYNC waitForFrameStart " << cycles;
   }
 }
 
@@ -139,15 +166,15 @@ void FrameManager::setState(FrameManager::State state)
 
       if (myTotalFrames > Metrics::initialGarbageFrames)
         myJitterEmulation.frameComplete(myCurrentFrameFinalLines,
-            static_cast<Int32>(myVsyncEnd - myVsyncStart));
+            static_cast<Int32>(myVsyncEnd - myVsyncStart), static_cast<Int32>(myVblankCycles));
 
       notifyFrameStart();
 
-      myVsyncLines = 0;
+      myVsyncLineCount = 0;
       break;
 
     case State::frame:
-      myVsyncLines = 0;
+      myVsyncLineCount = 0;
       myY = 0;
       break;
 
@@ -176,7 +203,7 @@ bool FrameManager::onSave(Serializer& out) const
 
   out.putInt(static_cast<uInt32>(myState));
   out.putInt(myLineInState);
-  out.putInt(myVsyncLines);
+  out.putInt(myVsyncLineCount);
   out.putInt(myY);
   out.putInt(myLastY);
 
@@ -200,7 +227,7 @@ bool FrameManager::onLoad(Serializer& in)
 
   myState = static_cast<State>(in.getInt());
   myLineInState = in.getInt();
-  myVsyncLines = in.getInt();
+  myVsyncLineCount = in.getInt();
   myY = in.getInt();
   myLastY = in.getInt();
 
diff --git a/src/emucore/tia/frame-manager/FrameManager.hxx b/src/emucore/tia/frame-manager/FrameManager.hxx
index 900bc3bae..6d71dc7fd 100644
--- a/src/emucore/tia/frame-manager/FrameManager.hxx
+++ b/src/emucore/tia/frame-manager/FrameManager.hxx
@@ -83,6 +83,8 @@ class FrameManager: public AbstractFrameManager {
 
     void setLayout(FrameLayout mode) override { layout(mode); }
 
+    void onSetVblank(uInt64 cycles) override;
+
     void onSetVsync(uInt64 cycles) override;
 
     void onNextLine() override;
@@ -116,7 +118,7 @@ class FrameManager: public AbstractFrameManager {
 
     State myState{State::waitForVsyncStart};
     uInt32 myLineInState{0};
-    uInt32 myVsyncLines{0};
+    uInt32 myVsyncLineCount{0};
     uInt32 myY{0}, myLastY{0};
 
     uInt32 myVblankLines{0};
@@ -129,6 +131,8 @@ class FrameManager: public AbstractFrameManager {
 
     uInt64 myVsyncStart{0};
     uInt64 myVsyncEnd{0};
+    uInt64 myVblankStart{0};
+    uInt64 myVblankCycles{0};
     bool myJitterEnabled{false};
 
     JitterEmulation myJitterEmulation;
diff --git a/src/emucore/tia/frame-manager/JitterEmulation.cxx b/src/emucore/tia/frame-manager/JitterEmulation.cxx
index 658557607..fc3758ec4 100644
--- a/src/emucore/tia/frame-manager/JitterEmulation.cxx
+++ b/src/emucore/tia/frame-manager/JitterEmulation.cxx
@@ -54,13 +54,16 @@ void JitterEmulation::setSensitivity(Int32 sensitivity)
 }
 
 // - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
-void JitterEmulation::frameComplete(Int32 scanlineCount, Int32 vsyncCycles)
+void JitterEmulation::frameComplete(Int32 scanlineCount, Int32 vsyncCycles, Int32 vblankCycles)
 {
 //#ifdef DEBUG_BUILD
 //  const int  vsyncLines = round((vsyncCycles - 2) / 76.0);
 //  cerr << "TV jitter " << myJitter << " - " << scanlineCount << ", " << vsyncCycles << ", " << vsyncLines << '\n';
 //#endif
 
+  if (mySensitivity >= 6)
+    vsyncCycles = std::min(vsyncCycles, vblankCycles);
+
   // Check if current frame size is stable compared to previous frame
   const bool scanlinesStable = scanlineCount == myLastFrameScanlines;
   const bool vsyncCyclesStable = vsyncCycles >= myVsyncCycles;
diff --git a/src/emucore/tia/frame-manager/JitterEmulation.hxx b/src/emucore/tia/frame-manager/JitterEmulation.hxx
index 89d13131c..eec2dbc33 100644
--- a/src/emucore/tia/frame-manager/JitterEmulation.hxx
+++ b/src/emucore/tia/frame-manager/JitterEmulation.hxx
@@ -48,7 +48,7 @@ class JitterEmulation : public Serializable
     void setRecovery(Int32 recoveryFactor) { myJitterRecovery = recoveryFactor; }
     void setYStart(Int32 ystart) { myYStart = ystart; }
 
-    void frameComplete(Int32 scanlineCount, Int32 vsyncCycles);
+    void frameComplete(Int32 scanlineCount, Int32 vsyncCycles, Int32 vblankCycles);
     Int32 jitter() const { return myJitter; }
 
     bool vsyncCorrect() const { return myVsyncCorrect; }