diff --git a/docs/rh-log.txt b/docs/rh-log.txt
index 6b287c387..ac304a52d 100644
--- a/docs/rh-log.txt
+++ b/docs/rh-log.txt
@@ -1,3 +1,12 @@
+September 22, 2009
+- Added a technique to try and minimize input lag with vsync enabled: Two
+  surfaces are alternately locked for read-only access each frame, forcing
+  the driver to stop buffering more than one frame at a time. The input lag
+  on my system doesn't seem to be as bad as it once was (I can no longer
+  see it obviously with my naked eye), but turning antilag on "feels"
+  slightly more responsive. The cvar d3d_antilag turns this technique on and
+  off. See <http://www.xyzw.de/c120.html> for more details.
+
 September 22, 2009  (Changes by Graf Zahl)
 - Added a check to Dehacked code which tries to set the blend color.
   It must set it to 0 if the alpha is 0 to avoid problems with special
diff --git a/src/win32/fb_d3d9.cpp b/src/win32/fb_d3d9.cpp
index 0cf47e9a6..562abf13d 100644
--- a/src/win32/fb_d3d9.cpp
+++ b/src/win32/fb_d3d9.cpp
@@ -246,6 +246,7 @@ CUSTOM_CVAR(Bool, vid_hw2d, true, CVAR_NOINITCALL)
 	BorderNeedRefresh = SB_state = screen->GetPageCount();
 }
 
+CVAR(Bool, d3d_antilag, true, CVAR_ARCHIVE|CVAR_GLOBALCONFIG)
 CVAR(Int, d3d_showpacks, 0, 0)
 CVAR(Bool, vid_hwaalines, true, CVAR_ARCHIVE|CVAR_GLOBALCONFIG)
 
@@ -276,6 +277,8 @@ D3DFB::D3DFB (int width, int height, bool fullscreen)
 	{
 		Shaders[i] = NULL;
 	}
+	BlockSurface[0] = NULL;
+	BlockSurface[1] = NULL;
 	FBFormat = D3DFMT_UNKNOWN;
 	PalFormat = D3DFMT_UNKNOWN;
 	VSync = vid_vsync;
@@ -531,6 +534,7 @@ bool D3DFB::CreateResources()
 	{
 		return false;
 	}
+	CreateBlockSurfaces();
 	return true;
 }
 
@@ -640,6 +644,8 @@ void D3DFB::ReleaseDefaultPoolItems()
 	SAFE_RELEASE( InitialWipeScreen );
 	SAFE_RELEASE( VertexBuffer );
 	SAFE_RELEASE( IndexBuffer );
+	SAFE_RELEASE( BlockSurface[0] );
+	SAFE_RELEASE( BlockSurface[1] );
 }
 
 //==========================================================================
@@ -674,10 +680,35 @@ bool D3DFB::Reset ()
 	{
 		return false;
 	}
+	CreateBlockSurfaces();
 	SetInitialState();
 	return true;
 }
 
+//==========================================================================
+//
+// D3DFB :: CreateBlockSurfaces
+//
+// Create blocking surfaces for antilag. It's okay if these can't be
+// created; antilag just won't work.
+//
+//==========================================================================
+
+void D3DFB::CreateBlockSurfaces()
+{
+	BlockNum = 0;
+	if (SUCCEEDED(D3DDevice->CreateOffscreenPlainSurface(16, 16, D3DFMT_A8R8G8B8,
+		D3DPOOL_DEFAULT, &BlockSurface[0], 0)))
+	{
+		if (FAILED(D3DDevice->CreateOffscreenPlainSurface(16, 16, D3DFMT_A8R8G8B8,
+			D3DPOOL_DEFAULT, &BlockSurface[1], 0)))
+		{
+			BlockSurface[0]->Release();
+			BlockSurface[0] = NULL;
+		}
+	}
+}
+
 //==========================================================================
 //
 // D3DFB :: KillNativePals
@@ -921,10 +952,7 @@ void D3DFB::Update ()
 			DrawRateStuff();
 			DrawPackedTextures(d3d_showpacks);
 			EndBatch();		// Make sure all batched primitives are drawn.
-			DoWindowedGamma();
-			D3DDevice->EndScene();
-			D3DDevice->Present(NULL, NULL, NULL, NULL);
-			InScene = false;
+			Flip();
 		}
 		In2D = 0;
 		return;
@@ -987,10 +1015,7 @@ void D3DFB::Update ()
 	Draw3DPart(In2D <= 1);
 	if (In2D == 0)
 	{
-		DoWindowedGamma();
-		D3DDevice->EndScene();
-		D3DDevice->Present(NULL, NULL, NULL, NULL);
-		InScene = false;
+		Flip();
 	}
 
 	BlitCycles.Unclock();
@@ -1000,6 +1025,30 @@ void D3DFB::Update ()
 	UpdatePending = false;
 }
 
+void D3DFB::Flip()
+{
+	assert(InScene);
+
+	DoWindowedGamma();
+	D3DDevice->EndScene();
+
+	// Attempt to counter input lag.
+	if (d3d_antilag && BlockSurface[0] != NULL)
+	{
+		D3DLOCKED_RECT lr;
+		volatile int dummy;
+		D3DDevice->ColorFill(BlockSurface[BlockNum], NULL, D3DCOLOR_ARGB(0xFF,0,0x20,0x50));
+		BlockNum ^= 1;
+		if (!FAILED((BlockSurface[BlockNum]->LockRect(&lr, NULL, D3DLOCK_READONLY))))
+		{
+			dummy = *(int *)lr.pBits;
+			BlockSurface[BlockNum]->UnlockRect();
+		}
+	}
+	D3DDevice->Present(NULL, NULL, NULL, NULL);
+	InScene = false;
+}
+
 bool D3DFB::PaintToWindow ()
 {
 	HRESULT hr;
diff --git a/src/win32/win32iface.h b/src/win32/win32iface.h
index 785664abd..e4c21a015 100644
--- a/src/win32/win32iface.h
+++ b/src/win32/win32iface.h
@@ -226,6 +226,7 @@ public:
 	bool Lock (bool buffered);
 	void Unlock ();
 	void Update ();
+	void Flip ();
 	PalEntry *GetPalette ();
 	void GetFlashedPalette (PalEntry palette[256]);
 	void UpdatePalette ();
@@ -332,6 +333,7 @@ private:
 	bool CreateResources();
 	void ReleaseResources();
 	bool LoadShaders();
+	void CreateBlockSurfaces();
 	bool CreateFBTexture();
 	bool CreatePaletteTexture();
 	bool CreateGrayPaletteTexture();
@@ -404,6 +406,7 @@ private:
 	bool SM14;
 	bool GatheringWipeScreen;
 	bool AALines;
+	BYTE BlockNum;
 	D3DPal *Palettes;
 	D3DTex *Textures;
 	PackingTexture *Packs;
@@ -427,6 +430,7 @@ private:
 
 	IDirect3DPixelShader9 *Shaders[NUM_SHADERS];
 
+	IDirect3DSurface9 *BlockSurface[2];
 	IDirect3DSurface9 *OldRenderTarget;
 	IDirect3DTexture9 *InitialWipeScreen, *FinalWipeScreen;