diff --git a/polymer/eduke32/build/include/build.h b/polymer/eduke32/build/include/build.h
index 8ceec8604..3fb13092d 100644
--- a/polymer/eduke32/build/include/build.h
+++ b/polymer/eduke32/build/include/build.h
@@ -99,6 +99,7 @@ void yax_setbunch(int16_t i, int16_t cf, int16_t bunchnum);
 void yax_setbunches(int16_t i, int16_t cb, int16_t fb);
 int16_t yax_getnextwall(int16_t wal, int16_t cf);
 void yax_setnextwall(int16_t wal, int16_t cf, int16_t thenextwall);
+int16_t yax_vnextsec(int16_t line, int16_t cf);
 void yax_update(int32_t resetstat);
 int32_t yax_getneighborsect(int32_t x, int32_t y, int32_t sectnum, int32_t cf, int16_t *ret_bunchnum);
 
diff --git a/polymer/eduke32/build/src/engine.c b/polymer/eduke32/build/src/engine.c
index 0802c3d38..8e4facf9c 100644
--- a/polymer/eduke32/build/src/engine.c
+++ b/polymer/eduke32/build/src/engine.c
@@ -261,9 +261,9 @@ void yax_updategrays(int32_t posze)
 int32_t g_nodraw = 0;
 int32_t scansector_retfast = 0;
 static int32_t scansector_collectsprites = 1;
-static int32_t yax_globalcf = -1;
-static int32_t yax_globallev = YAX_MAXDRAWS;
-static int32_t yax_globalbunch = -1;
+static int32_t yax_globalcf = -1, yax_nomaskpass=0;
+int32_t yax_globallev = YAX_MAXDRAWS;
+int32_t yax_globalbunch = -1;
 
 // duplicated tsprites
 //  [i]:
@@ -277,11 +277,16 @@ static int16_t yax_tsprite[1 + 2*YAX_MAXDRAWS][MAXSPRITESONSCREEN];
 int16_t yax_bunchnum[MAXSECTORS][2];
 int16_t yax_nextwall[MAXWALLS][2];
 
-static int32_t yax_islockededge(int16_t line, int16_t cf)
+static int32_t yax_islockededge(int32_t line, int32_t cf)
 {
     return !!(wall[line].cstat&(YAX_NEXTWALLBIT(cf)));
 }
 
+static int32_t yax_isislandwall(int32_t line, int32_t cf)
+{
+    return (yax_vnextsec(line, cf)>=0);
+}
+
 #define YAX_BUNCHNUM(Sect, Cf) (*(&sector[Sect].ceilingxpanning + 8*Cf))
 
 //// bunch getters/setters
@@ -374,6 +379,19 @@ void yax_setnextwall(int16_t wal, int16_t cf, int16_t thenextwall)
     }
 }
 
+// make one step in the vertical direction, and if the wall we arrive at
+// is red, return its nextsector.
+int16_t yax_vnextsec(int16_t line, int16_t cf)
+{
+    int16_t ynw = yax_getnextwall(line, cf);
+
+    if (ynw < 0)
+        return -1;
+
+    return wall[ynw].nextsector;
+}
+
+
 //// in-struct --> array transfer (only resetstat==0); list construction
 // resetstat:  0: reset and read data from structs and construct linked lists etc.
 //             1: only reset
@@ -4607,11 +4625,9 @@ static void drawalls(int32_t bunch)
                 }
             }
         }
+
         if ((nextsectnum < 0) || (wal->cstat&32))   //White/1-way wall
         {
-#ifdef YAX_ENABLE
-            int16_t ynw[2];
-#endif
             globalorientation = (int32_t)wal->cstat;
             if (nextsectnum < 0) globalpicnum = wal->picnum;
             else globalpicnum = wal->overpicnum;
@@ -4643,14 +4659,11 @@ static void drawalls(int32_t bunch)
 
             if (gotswall == 0) { gotswall = 1; prepwall(z,wal); }
             wallscan(x1,x2,uplc,dplc,swall,lwall);
+
 #ifdef YAX_ENABLE
             // TODO: slopes?
-            ynw[0] = yax_getnextwall(wallnum, 0);
-            ynw[1] = yax_getnextwall(wallnum, 1);
 
-            if (globalposz > sec->floorz && ((ynw[1]>=0 && wall[ynw[1]].nextwall>=0)
-//                                             || (nextsectnum>=0 && yax_getbunch(sectnum,1)>=0)
-                    ))
+            if (globalposz > sec->floorz && yax_isislandwall(wallnum, YAX_FLOOR))
             {
                 for (x=x1; x<=x2; x++)
                     if (dplc[x] > umost[x] && umost[x] <= dmost[x])
@@ -4659,9 +4672,7 @@ static void drawalls(int32_t bunch)
                         if (umost[x] > dmost[x]) numhits--;
                     }
             }
-            else if (globalposz < sec->ceilingz && ((ynw[0]>=0 && wall[ynw[0]].nextwall>=0)
-//                                                    || (nextsectnum>=0 && yax_getbunch(sectnum,0)>=0)
-                         ))
+            else if (globalposz < sec->ceilingz && yax_isislandwall(wallnum, YAX_CEILING))
             {
                 for (x=x1; x<=x2; x++)
                     if (uplc[x] < dmost[x] && umost[x] <= dmost[x])
diff --git a/polymer/eduke32/build/src/engine_priv.h b/polymer/eduke32/build/src/engine_priv.h
index e725d54e4..69bdc0210 100644
--- a/polymer/eduke32/build/src/engine_priv.h
+++ b/polymer/eduke32/build/src/engine_priv.h
@@ -76,8 +76,9 @@ int32_t animateoffs(int16_t tilenum, int16_t fakevar);
 extern void polymost_scansector(int32_t sectnum);
 #endif
 int32_t engine_addtsprite(int16_t z, int16_t sectnum);
-extern int32_t g_nodraw, scansector_retfast;
 #ifdef YAX_ENABLE
+extern int32_t g_nodraw, scansector_retfast;
+extern int32_t yax_globallev, yax_globalbunch;
 extern uint8_t haveymost[YAX_MAXBUNCHES>>3];
 #endif