diff --git a/specs/udmf_zdoom.txt b/specs/udmf_zdoom.txt
index 9d7bb3caf..bdd70322e 100644
--- a/specs/udmf_zdoom.txt
+++ b/specs/udmf_zdoom.txt
@@ -141,6 +141,9 @@ Note: All <bool> fields default to false unless mentioned otherwise.
       light = <integer>;        // This side's light level. Default is 0.
       lightabsolute = <bool>;   // true = 'light' is an absolute value. Default is 
                                 // relative to the owning sector's light level.
+      lightfog = <bool>;        // true = This side's relative lighting is used even in
+                                // foggy sectors. Default is to disable relative
+                                // lighting in foggy sectors.
       nofakecontrast = <bool>;  // Disables use of fake contrast on this sidedef.
       smoothlighting = <bool>;  // Use smooth fake contrast.
       clipmidtex = <bool>;      // Side's mid textures are clipped to floor and ceiling.
diff --git a/src/namedef.h b/src/namedef.h
index 50fa9f292..34f9b7235 100644
--- a/src/namedef.h
+++ b/src/namedef.h
@@ -448,6 +448,7 @@ xx(scalex_bottom)
 xx(scaley_bottom)
 xx(light)
 xx(lightabsolute)
+xx(lightfog)
 xx(nofakecontrast)
 xx(smoothlighting)
 xx(blockprojectiles)
diff --git a/src/p_sectors.cpp b/src/p_sectors.cpp
index 330344679..d90466fec 100644
--- a/src/p_sectors.cpp
+++ b/src/p_sectors.cpp
@@ -996,10 +996,10 @@ int side_t::GetLightLevel (bool foggy, int baselight, bool noabsolute, int *pfak
 				baselight += rel;
 			}
 		}
-		if (!(Flags & WALLF_ABSLIGHTING))
-		{
-			baselight += this->Light;
-		}
+	}
+	if (!(Flags & WALLF_ABSLIGHTING) && (!foggy || (Flags & WALLF_LIGHT_FOG)))
+	{
+		baselight += this->Light;
 	}
 	return baselight;
 }
diff --git a/src/p_udmf.cpp b/src/p_udmf.cpp
index 2bc3e0bea..5abe40908 100644
--- a/src/p_udmf.cpp
+++ b/src/p_udmf.cpp
@@ -1053,6 +1053,10 @@ public:
 				Flag(sd->Flags, WALLF_ABSLIGHTING, key);
 				continue;
 
+			case NAME_lightfog:
+				Flag(sd->Flags, WALLF_LIGHT_FOG, key);
+				continue;
+
 			case NAME_nofakecontrast:
 				Flag(sd->Flags, WALLF_NOFAKECONTRAST, key);
 				continue;
diff --git a/src/r_defs.h b/src/r_defs.h
index 5f8272b3d..87c9e9e4f 100644
--- a/src/r_defs.h
+++ b/src/r_defs.h
@@ -744,6 +744,7 @@ enum
 	WALLF_CLIP_MIDTEX	 = 16,	// Like the line counterpart, but only for this side.
 	WALLF_WRAP_MIDTEX	 = 32,	// Like the line counterpart, but only for this side.
 	WALLF_POLYOBJ		 = 64,	// This wall belongs to a polyobject.
+	WALLF_LIGHT_FOG      = 128,	// This wall's Light is used even in fog.
 };
 
 struct side_t