diff --git a/src/swrenderer/line/r_walldraw.cpp b/src/swrenderer/line/r_walldraw.cpp
index 64f14135f4..92235ae344 100644
--- a/src/swrenderer/line/r_walldraw.cpp
+++ b/src/swrenderer/line/r_walldraw.cpp
@@ -189,7 +189,12 @@ namespace swrenderer
 		{
 			auto viewport = Thread->Viewport.get();
 			
-			drawerargs.dc_viewpos.X = (float)((x + 0.5 - viewport->CenterX) / viewport->CenterX * zcol);
+			int tx = x;
+			bool mirror = !!(Thread->Portal->MirrorFlags & RF_XFLIP);
+			if (mirror)
+				tx = viewwidth - tx - 1;
+
+			drawerargs.dc_viewpos.X = (float)((tx + 0.5 - viewport->CenterX) / viewport->CenterX * zcol);
 			drawerargs.dc_viewpos.Y = zcol;
 			drawerargs.dc_viewpos.Z = (float)((viewport->CenterY - y1 - 0.5) / viewport->InvZtoScale * zcol);
 			drawerargs.dc_viewpos_step.Z = (float)(-zcol / viewport->InvZtoScale);
diff --git a/src/swrenderer/plane/r_flatplane.cpp b/src/swrenderer/plane/r_flatplane.cpp
index 8d01205599..88b3871a6a 100644
--- a/src/swrenderer/plane/r_flatplane.cpp
+++ b/src/swrenderer/plane/r_flatplane.cpp
@@ -205,13 +205,21 @@ namespace swrenderer
 
 		if (r_dynlights)
 		{
+			int tx = x1;
+			bool mirror = !!(Thread->Portal->MirrorFlags & RF_XFLIP);
+			if (mirror)
+				tx = viewwidth - tx - 1;
+
 			// Find row position in view space
 			float zspan = (float)(planeheight / (fabs(y + 0.5 - viewport->CenterY) / viewport->InvZtoScale));
-			drawerargs.dc_viewpos.X = (float)((x1 + 0.5 - viewport->CenterX) / viewport->CenterX * zspan);
+			drawerargs.dc_viewpos.X = (float)((tx + 0.5 - viewport->CenterX) / viewport->CenterX * zspan);
 			drawerargs.dc_viewpos.Y = zspan;
 			drawerargs.dc_viewpos.Z = (float)((viewport->CenterY - y - 0.5) / viewport->InvZtoScale * zspan);
 			drawerargs.dc_viewpos_step.X = (float)(zspan / viewport->CenterX);
 
+			if (mirror)
+				drawerargs.dc_viewpos_step.X = -drawerargs.dc_viewpos_step.X;
+
 			// Plane normal
 			drawerargs.dc_normal.X = 0.0f;
 			drawerargs.dc_normal.Y = 0.0f;