diff --git a/src/d_main.c b/src/d_main.c
index f611c4c3f..d24cc4b58 100644
--- a/src/d_main.c
+++ b/src/d_main.c
@@ -155,7 +155,6 @@ event_t events[MAXEVENTS];
 INT32 eventhead, eventtail;
 
 boolean dedicated = false;
-boolean tic_happened = false; // Frame interpolation/uncapped
 
 //
 // D_PostEvent
@@ -773,13 +772,25 @@ void D_SRB2Loop(void)
 			realtics = 1;
 
 		// process tics (but maybe not if realtic == 0)
-		tic_happened = realtics ? true : false;
 		TryRunTics(realtics);
 
 		if (cv_frameinterpolation.value == 1)
-			rendertimefrac = I_GetTimeFrac();
+		{
+			fixed_t entertimefrac = I_GetTimeFrac();
+			// renderdeltatics is a bit awkard to evaluate, since the system time interface is whole tic-based
+			renderdeltatics = realtics * FRACUNIT;
+			if (entertimefrac > rendertimefrac)
+				renderdeltatics += entertimefrac - rendertimefrac;
+			else
+				renderdeltatics -= rendertimefrac - entertimefrac;
+
+			rendertimefrac = entertimefrac;
+		}
 		else
+		{
 			rendertimefrac = FRACUNIT;
+			renderdeltatics = realtics * FRACUNIT;
+		}
 
 		if (cv_frameinterpolation.value == 1)
 		{
diff --git a/src/d_main.h b/src/d_main.h
index 26b5c4528..81de0634d 100644
--- a/src/d_main.h
+++ b/src/d_main.h
@@ -26,7 +26,6 @@ extern char srb2home[256]; //Alam: My Home
 extern boolean usehome; //Alam: which path?
 extern const char *pandf; //Alam: how to path?
 extern char srb2path[256]; //Alam: SRB2's Home
-extern boolean tic_happened; // Frame interpolation/uncapped
 
 // the infinite loop of D_SRB2Loop() called from win_main for windows version
 void D_SRB2Loop(void) FUNCNORETURN;
diff --git a/src/hardware/hw_main.c b/src/hardware/hw_main.c
index 997978a31..e3f56f831 100644
--- a/src/hardware/hw_main.c
+++ b/src/hardware/hw_main.c
@@ -6687,7 +6687,6 @@ INT32 HWR_GetTextureUsed(void)
 void HWR_DoPostProcessor(player_t *player)
 {
 	postimg_t *type = &postimgtype[0];
-	fixed_t fractime;
 	SINT8 i;
 
 	HWD.pfnUnSetShader();
@@ -6739,7 +6738,7 @@ void HWR_DoPostProcessor(player_t *player)
 		// 10 by 10 grid. 2 coordinates (xy)
 		float v[SCREENVERTS][SCREENVERTS][2];
 		static double disStart = 0;
-		static float last_fractime = 0;
+		static fixed_t last_fractime = 0;
 
 		UINT8 x, y;
 		INT32 WAVELENGTH;
@@ -6772,16 +6771,15 @@ void HWR_DoPostProcessor(player_t *player)
 		HWD.pfnPostImgRedraw(v);
 		if (!(paused || P_AutoPause()))
 			disStart += 1;
-		fractime = I_GetTimeFrac();
-		if (tic_happened)
+		if (renderdeltatics > FRACUNIT)
 		{
-			disStart = disStart - last_fractime + 1 + FIXED_TO_FLOAT(fractime);
+			disStart = disStart - FIXED_TO_FLOAT(last_fractime) + 1 + FIXED_TO_FLOAT(rendertimefrac);
 		}
 		else
 		{
-			disStart = disStart - last_fractime + FIXED_TO_FLOAT(fractime);
+			disStart = disStart - FIXED_TO_FLOAT(last_fractime) + FIXED_TO_FLOAT(rendertimefrac);
 		}
-		last_fractime = fractime;
+		last_fractime = rendertimefrac;
 
 		// Capture the screen again for screen waving on the intermission
 		if(gamestate != GS_INTERMISSION)
diff --git a/src/r_main.c b/src/r_main.c
index 6cb05801c..231bde280 100644
--- a/src/r_main.c
+++ b/src/r_main.c
@@ -81,6 +81,7 @@ mobj_t *r_viewmobj;
 int r_splitscreen;
 
 fixed_t rendertimefrac;
+fixed_t renderdeltatics;
 
 //
 // precalculated math tables
diff --git a/src/r_main.h b/src/r_main.h
index 2ddec0ff1..a2acf60d9 100644
--- a/src/r_main.h
+++ b/src/r_main.h
@@ -33,7 +33,10 @@ extern fixed_t fovtan[MAXSPLITSCREENPLAYERS];
 
 extern size_t validcount, linecount, loopcount, framecount;
 
+// The fraction of a tic being drawn (for interpolation between two tics)
 extern fixed_t rendertimefrac;
+// Evaluated delta tics for this frame (how many tics since the last frame)
+extern fixed_t renderdeltatics;;
 
 //
 // Lighting LUT.