diff --git a/docs/rh-log.txt b/docs/rh-log.txt
index 62db7c87c..f9282cd59 100644
--- a/docs/rh-log.txt
+++ b/docs/rh-log.txt
@@ -1,4 +1,6 @@
 February 28, 2008
+- Fixed: The colormap changes by column, so the assembly rt_* routines need
+  to be setup for every column group, not once per image.
 - Fixed: rt_Translate1col() had a couple of bugs.
 
 February 27, 2008
diff --git a/src/r_draw.cpp b/src/r_draw.cpp
index 410cfb956..3ec52210a 100644
--- a/src/r_draw.cpp
+++ b/src/r_draw.cpp
@@ -80,9 +80,6 @@ int				detailyshift;		// [RH] Y shift for vertical detail level
 extern "C" void STACK_ARGS DoubleHoriz_MMX (int height, int width, BYTE *dest, int pitch);
 extern "C" void STACK_ARGS DoubleHorizVert_MMX (int height, int width, BYTE *dest, int pitch);
 extern "C" void STACK_ARGS DoubleVert_ASM (int height, int width, BYTE *dest, int pitch);
-extern "C" void R_SetupShadedCol();
-extern "C" void R_SetupAddCol();
-extern "C" void R_SetupAddClampCol();
 #endif
 
 // [RH] Pointers to the different column drawers.
@@ -2273,9 +2270,6 @@ ESPSResult R_SetPatchStyle (FRenderStyle style, fixed_t alpha, int translation,
 		{
 			dc_colormap += fixedlightlev;
 		}
-#ifdef USEASM
-		R_SetupShadedCol();
-#endif
 		return r_columnmethod ? DoDraw1 : DoDraw0;
 	}
 
@@ -2307,16 +2301,6 @@ ESPSResult R_SetPatchStyle (FRenderStyle style, fixed_t alpha, int translation,
 	{
 		return DontDraw;
 	}
-#ifdef USEASM
-	if (hcolfunc_post4 == rt_addclamp4cols || hcolfunc_post4 == rt_tlateaddclamp4cols)
-	{
-		R_SetupAddClampCol();
-	}
-	else if (hcolfunc_post4 == rt_add4cols || hcolfunc_post4 == rt_tlateadd4cols)
-	{
-		R_SetupAddCol();
-	}
-#endif
 	return r_columnmethod ? DoDraw1 : DoDraw0;
 }
 
diff --git a/src/r_drawt.cpp b/src/r_drawt.cpp
index e0a3711a1..73cd50b01 100644
--- a/src/r_drawt.cpp
+++ b/src/r_drawt.cpp
@@ -59,6 +59,12 @@ unsigned int dc_tspans[4][MAXHEIGHT];
 unsigned int *dc_ctspan[4];
 unsigned int *horizspan[4];
 
+#ifdef USEASM
+extern "C" void R_SetupShadedCol();
+extern "C" void R_SetupAddCol();
+extern "C" void R_SetupAddClampCol();
+#endif
+
 #ifndef USEASM
 // Copies one span at hx to the screen at sx.
 void rt_copy1col_c (int hx, int sx, int yl, int yh)
@@ -844,6 +850,22 @@ void rt_draw4cols (int sx)
 		dc_ctspan[x][1] = screen->GetHeight();
 	}
 
+#ifdef USEASM
+	// Setup assembly routines for changed colormaps or other parameters.
+	if (hcolfunc_post4 == rt_shaded4cols)
+	{
+		R_SetupShadedCol();
+	}
+	else if (hcolfunc_post4 == rt_addclamp4cols || hcolfunc_post4 == rt_tlateaddclamp4cols)
+	{
+		R_SetupAddClampCol();
+	}
+	else if (hcolfunc_post4 == rt_add4cols || hcolfunc_post4 == rt_tlateadd4cols)
+	{
+		R_SetupAddCol();
+	}
+#endif
+
 	for (;;)
 	{
 		// If a column is out of spans, mark it as such
diff --git a/src/tmap.nas b/src/tmap.nas
index 7c4b44231..82cc113a3 100644
--- a/src/tmap.nas
+++ b/src/tmap.nas
@@ -1745,17 +1745,21 @@ GLOBAL	@R_SetupShadedCol@0
 R_SetupShadedCol:
 @R_SetupShadedCol@0:
 		mov		eax,[dc_colormap]
+		cmp		[s4cm1+3],eax
+		je		.cmdone
 		mov		[s4cm1+3],eax
 		mov		[s4cm2+3],eax
 		mov		[s4cm3+3],eax
 		mov		[s4cm4+3],eax
-		mov		eax,[dc_color]
+.cmdone	mov		eax,[dc_color]
 		lea		eax,[Col2RGB8+eax*4]
+		cmp		[s4fg1+3],eax
+		je		.cdone
 		mov		[s4fg1+3],eax
 		mov		[s4fg2+3],eax
 		mov		[s4fg3+3],eax
 		mov		[s4fg4+3],eax
-		ret
+.cdone	ret
 
 GLOBAL	R_SetupAddCol
 GLOBAL	@R_SetupAddCol@0
@@ -1766,21 +1770,27 @@ GLOBAL	@R_SetupAddCol@0
 R_SetupAddCol:
 @R_SetupAddCol@0:
 		mov		eax,[dc_colormap]
+		cmp		[a4cm1+3],eax
+		je		.cmdone
 		mov		[a4cm1+3],eax
 		mov		[a4cm2+3],eax
 		mov		[a4cm3+3],eax
 		mov		[a4cm4+3],eax
-		mov		eax,[dc_srcblend]
+.cmdone	mov		eax,[dc_srcblend]
+		cmp		[a4fg1+3],eax
+		je		.sbdone
 		mov		[a4fg1+3],eax
 		mov		[a4fg2+3],eax
 		mov		[a4fg3+3],eax
 		mov		[a4fg4+3],eax
-		mov		eax,[dc_destblend]
+.sbdone	mov		eax,[dc_destblend]
+		cmp		[a4bg1+3],eax
+		je		.dbdone
 		mov		[a4bg1+3],eax
 		mov		[a4bg2+3],eax
 		mov		[a4bg3+3],eax
 		mov		[a4bg4+3],eax
-		ret
+.dbdone	ret
 
 GLOBAL	R_SetupAddClampCol
 GLOBAL	@R_SetupAddClampCol@0
@@ -1791,21 +1801,27 @@ GLOBAL	@R_SetupAddClampCol@0
 R_SetupAddClampCol:
 @R_SetupAddClampCol@0:
 		mov		eax,[dc_colormap]
+		cmp		[a4cm1+3],eax
+		je		.cmdone
 		mov		[ac4cm1+3],eax
 		mov		[ac4cm2+3],eax
 		mov		[ac4cm3+3],eax
 		mov		[ac4cm4+3],eax
-		mov		eax,[dc_srcblend]
+.cmdone	mov		eax,[dc_srcblend]
+		cmp		[ac4fg1+3],eax
+		je		.sbdone
 		mov		[ac4fg1+3],eax
 		mov		[ac4fg2+3],eax
 		mov		[ac4fg3+3],eax
 		mov		[ac4fg4+3],eax
-		mov		eax,[dc_destblend]
+.sbdone	mov		eax,[dc_destblend]
+		cmp		[ac4bg1+3],eax
+		je		.dbdone
 		mov		[ac4bg1+3],eax
 		mov		[ac4bg2+3],eax
 		mov		[ac4bg3+3],eax
 		mov		[ac4bg4+3],eax
-		ret
+.dbdone	ret
 
 EXTERN setvlinebpl_
 EXTERN setpitch3
@@ -1827,14 +1843,9 @@ _ASM_PatchPitch:
 		mov		ecx,eax
 		neg		ecx
 		inc		ecx
-;		mov		[a4p1+2],ecx
 		inc		ecx
-;		mov		[a4p2a+3],ecx
-;		mov		[a4p2b+2],ecx
 		mov		[s4p2+2],ecx
 		inc		ecx
-;		mov		[a4p3a+3],ecx
-;		mov		[a4p3b+2],ecx
 		mov		[s4p3+2],ecx
 		call	setpitch3
 		jmp		setvlinebpl_