diff --git a/common/main/wall.h b/common/main/wall.h
index ccffe7663..2c268e7ba 100644
--- a/common/main/wall.h
+++ b/common/main/wall.h
@@ -101,21 +101,21 @@ struct vobjptridx_t;
 #endif
 
 // WALL_IS_DOORWAY flags.
-#define WID_FLY_FLAG            1
-#define WID_RENDER_FLAG         2
-#define WID_RENDPAST_FLAG       4
-#define WID_EXTERNAL_FLAG       8
+static const unsigned WID_FLY_FLAG           = 1;
+static const unsigned WID_RENDER_FLAG        = 2;
+static const unsigned WID_RENDPAST_FLAG      = 4;
+static const unsigned WID_EXTERNAL_FLAG      = 8;
 #if defined(DXX_BUILD_DESCENT_II)
-#define WID_CLOAKED_FLAG        16
+static const unsigned WID_CLOAKED_FLAG       = 16;
 #endif
 
 //  WALL_IS_DOORWAY return values          F/R/RP
-#define WID_WALL                    2   // 0/1/0        wall
-#define WID_TRANSPARENT_WALL        6   // 0/1/1        transparent wall
-#define WID_ILLUSORY_WALL           3   // 1/1/0        illusory wall
-#define WID_TRANSILLUSORY_WALL      7   // 1/1/1        transparent illusory wall
-#define WID_NO_WALL                 5   //  1/0/1       no wall, can fly through
-#define WID_EXTERNAL                8   // 0/0/0/1  don't see it, dont fly through it
+static const unsigned WID_WALL                   = WID_RENDER_FLAG;   // 0/1/0        wall
+static const unsigned WID_TRANSPARENT_WALL       = WID_RENDER_FLAG | WID_RENDPAST_FLAG;   // 0/1/1        transparent wall
+static const unsigned WID_ILLUSORY_WALL          = WID_FLY_FLAG | WID_RENDPAST_FLAG;   // 1/1/0        illusory wall
+static const unsigned WID_TRANSILLUSORY_WALL     = WID_FLY_FLAG | WID_RENDER_FLAG | WID_RENDPAST_FLAG;   // 1/1/1        transparent illusory wall
+static const unsigned WID_NO_WALL                = WID_FLY_FLAG | WID_RENDPAST_FLAG;   //  1/0/1       no wall, can fly through
+static const unsigned WID_EXTERNAL               = WID_EXTERNAL_FLAG;   // 0/0/0/1  don't see it, dont fly through it
 
 #define MAX_STUCK_OBJECTS   32
 
diff --git a/similar/main/gameseg.cpp b/similar/main/gameseg.cpp
index d3d007358..c3c98d652 100644
--- a/similar/main/gameseg.cpp
+++ b/similar/main/gameseg.cpp
@@ -1871,9 +1871,13 @@ static void ambient_mark_bfs(segnum_t segnum, sbyte *marked_segs, int depth)
 	marked_segs[segnum] = 1;
 
 	for (i=0; i<MAX_SIDES_PER_SEGMENT; i++) {
-		int	child = Segments[segnum].children[i];
+		auto	child = Segments[segnum].children[i];
 
-		if (IS_CHILD(child) && (WALL_IS_DOORWAY(&Segments[segnum],i) & WID_RENDPAST_FLAG) && !marked_segs[child])
+		/*
+		 * No explicit check for IS_CHILD.  If !IS_CHILD, then
+		 * WALL_IS_DOORWAY never sets WID_RENDPAST_FLAG.
+		 */
+		if ((WALL_IS_DOORWAY(&Segments[segnum],i) & WID_RENDPAST_FLAG) && !marked_segs[child])
 			ambient_mark_bfs(child, marked_segs, depth-1);
 	}