diff --git a/plow/PlowMain.c b/plow/PlowMain.c
index a2bca847..36980ae9 100644
--- a/plow/PlowMain.c
+++ b/plow/PlowMain.c
@@ -1043,7 +1043,7 @@ plowSelPaintPlow(rect, type, distance)
     plowAtomize(DBPlane(type), &plowLHS, plowSelPaintAdd, (ClientData) NULL);
 #endif	/* notdef */
     plowLHS.r_xbot--;
-    plowSrShadow(DBPlane(type), &plowLHS, DBZeroTypeBits,
+    plowSrShadow(DBPlane(type), &plowLHS, &DBZeroTypeBits,
 			plowInitialPaint, INT2CD(plowLHS.r_xtop));
 
     /* Queue the RHS */
@@ -1054,7 +1054,7 @@ plowSelPaintPlow(rect, type, distance)
 #endif	/* notdef */
     plowRHS.r_xbot--;
     TTMaskSetOnlyType(&mask, type);
-    plowSrShadow(DBPlane(type), &plowRHS, mask,
+    plowSrShadow(DBPlane(type), &plowRHS, &mask,
 			plowInitialPaint, INT2CD(plowRHS.r_xtop));
 
     return (0);
diff --git a/plow/PlowRules1.c b/plow/PlowRules1.c
index 17d96ae5..b9419f6f 100644
--- a/plow/PlowRules1.c
+++ b/plow/PlowRules1.c
@@ -87,7 +87,7 @@ prClearUmbra(edge)
     ar.ar_moving = edge;
     ar.ar_rule = (PlowRule *) NULL;
     (void) plowSrShadow(edge->e_pNum, &edge->e_rect,
-		rhsTypes, plowApplyRule, (ClientData) &ar);
+		&rhsTypes, plowApplyRule, (ClientData) &ar);
 }
 
 /*
@@ -138,7 +138,7 @@ prUmbra(edge, rules)
 	ar.ar_rule = pr;
 	searchArea.r_xtop = edge->e_newx + pr->pr_dist;
 	(void) plowSrShadow(pr->pr_pNum, &searchArea,
-			pr->pr_oktypes, plowApplyRule, (ClientData) &ar);
+			&pr->pr_oktypes, plowApplyRule, (ClientData) &ar);
     }
 }
 
@@ -342,7 +342,7 @@ plowPenumbraTopProc(outline, ar)
 	    searchArea.r_ybot = outline->o_rect.r_ytop;
 	    searchArea.r_ytop = ar->ar_clip.p_y;
 	    (void) plowSrShadow(pr->pr_pNum,
-		&searchArea, pr->pr_oktypes, plowPenumbraRule,
+		&searchArea, &pr->pr_oktypes, plowPenumbraRule,
 		(ClientData) ar);
 	}
 	return (1);
@@ -350,7 +350,7 @@ plowPenumbraTopProc(outline, ar)
 
     /* Shadow search to right of this segment of the penumbra boundary */
     (void) plowSrShadow(pr->pr_pNum, &searchArea,
-		pr->pr_oktypes, plowApplyRule, (ClientData) ar);
+		&pr->pr_oktypes, plowApplyRule, (ClientData) ar);
     return (ret);
 }
 
@@ -396,7 +396,7 @@ plowPenumbraBotProc(outline, ar)
 	    searchArea.r_ybot = ar->ar_clip.p_y;
 	    searchArea.r_ytop = outline->o_rect.r_ybot;
 	    (void) plowSrShadow(pr->pr_pNum,
-		&searchArea, pr->pr_oktypes, plowPenumbraRule,
+		&searchArea, &pr->pr_oktypes, plowPenumbraRule,
 		(ClientData) ar);
 	}
 	return (1);
@@ -404,7 +404,7 @@ plowPenumbraBotProc(outline, ar)
 
     /* Shadow search to right of this segment of the penumbra boundary */
     (void) plowSrShadow(pr->pr_pNum, &searchArea,
-		pr->pr_oktypes, plowApplyRule, (ClientData) ar);
+		&pr->pr_oktypes, plowApplyRule, (ClientData) ar);
 
     return (ret);
 }
diff --git a/plow/PlowRules2.c b/plow/PlowRules2.c
index b3b3f81e..c4b70b0f 100644
--- a/plow/PlowRules2.c
+++ b/plow/PlowRules2.c
@@ -231,7 +231,7 @@ prFixedPenumbraTop(edge)
     for ( ; pr; pr = pr->pr_next)
     {
 	searchRect.r_ytop = edge->e_ytop + pr->pr_dist;
-	(void) plowSrShadow(pr->pr_pNum, &searchRect, pr->pr_oktypes,
+	(void) plowSrShadow(pr->pr_pNum, &searchRect, &pr->pr_oktypes,
 		plowApplyRule, (ClientData) &ar);
     }
 }
@@ -261,7 +261,7 @@ prFixedPenumbraBot(edge)
     for ( ; pr; pr = pr->pr_next)
     {
 	searchRect.r_ybot = edge->e_ybot - pr->pr_dist;
-	(void) plowSrShadow(pr->pr_pNum, &searchRect, pr->pr_oktypes,
+	(void) plowSrShadow(pr->pr_pNum, &searchRect, &pr->pr_oktypes,
 		plowApplyRule, (ClientData) &ar);
     }
     return 0;
@@ -493,13 +493,13 @@ prCoverTop(edge)
     for (pr = plowWidthRulesTbl[ltype][rtype]; pr; pr = pr->pr_next)
     {
 	searchArea.r_ytop = edge->e_ytop + pr->pr_dist;
-	(void) plowSrShadow(edge->e_pNum, &searchArea, pr->pr_oktypes,
+	(void) plowSrShadow(edge->e_pNum, &searchArea, &pr->pr_oktypes,
 		plowApplyRule, (ClientData) &ar);
     }
     for (pr = plowSpacingRulesTbl[ltype][rtype]; pr; pr = pr->pr_next)
     {
 	searchArea.r_ytop = edge->e_ytop + pr->pr_dist;
-	(void) plowSrShadow(edge->e_pNum, &searchArea, pr->pr_oktypes,
+	(void) plowSrShadow(edge->e_pNum, &searchArea, &pr->pr_oktypes,
 		plowApplyRule, (ClientData) &ar);
     }
 }
@@ -531,13 +531,13 @@ prCoverBot(edge)
     for (pr = plowWidthRulesTbl[ltype][rtype]; pr; pr = pr->pr_next)
     {
 	searchArea.r_ybot = edge->e_ybot - pr->pr_dist;
-	(void) plowSrShadow(edge->e_pNum, &searchArea, pr->pr_oktypes,
+	(void) plowSrShadow(edge->e_pNum, &searchArea, &pr->pr_oktypes,
 		plowApplyRule, (ClientData) &ar);
     }
     for (pr = plowSpacingRulesTbl[ltype][rtype]; pr; pr = pr->pr_next)
     {
 	searchArea.r_ybot = edge->e_ybot - pr->pr_dist;
-	(void) plowSrShadow(edge->e_pNum, &searchArea, pr->pr_oktypes,
+	(void) plowSrShadow(edge->e_pNum, &searchArea, &pr->pr_oktypes,
 		plowApplyRule, (ClientData) &ar);
     }
     return 0;
@@ -919,7 +919,7 @@ prCell(edge)
 	(void) DBSrPaintArea((Tile *) NULL, plowYankDef->cd_planes[pNum],
 		&ar.ar_search, &DBAllTypeBits,
 		plowCellDragPaint, (ClientData) &ar);
-	(void) plowSrShadow(pNum, &shadowArea, DBZeroTypeBits,
+	(void) plowSrShadow(pNum, &shadowArea, &DBZeroTypeBits,
 		plowCellPushPaint, (ClientData) &ar);
     }
 
diff --git a/plow/PlowRules3.c b/plow/PlowRules3.c
index 0001171a..bd731553 100644
--- a/plow/PlowRules3.c
+++ b/plow/PlowRules3.c
@@ -248,7 +248,7 @@ scanDown(inarg, type, canMoveInargEdge)
 	ar.ar_moving = movingEdge;
 	ar.ar_rule = (PlowRule *) NULL;
 	plowSrShadow(movingEdge->e_pNum, &shadowRect,
-		DBZeroTypeBits, plowApplyRule, (ClientData) &ar);
+		&DBZeroTypeBits, plowApplyRule, (ClientData) &ar);
     }
 #endif	/* notdef */
     return 0;
@@ -343,7 +343,7 @@ scanUp(inarg, type, canMoveInargEdge)
 	ar.ar_moving = movingEdge;
 	ar.ar_rule = (PlowRule *) NULL;
 	plowSrShadow(movingEdge->e_pNum, &shadowRect,
-		DBZeroTypeBits, plowApplyRule, (ClientData) &ar);
+		&DBZeroTypeBits, plowApplyRule, (ClientData) &ar);
     }
 #endif	/* notdef */
     return 0;
diff --git a/plow/PlowSearch.c b/plow/PlowSearch.c
index 199e2a1f..7105d7b4 100644
--- a/plow/PlowSearch.c
+++ b/plow/PlowSearch.c
@@ -203,16 +203,17 @@ switch ((o)->o_nextDir) \
  */
 
 int
-plowSrShadow(pNum, area, okTypes, proc, cdata)
-    int pNum;			/* Plane from plowYankDef to search */
-    Rect *area;			/* Area to search.  Edges coincident with the
+plowSrShadow(
+    int pNum,			/* Plane from plowYankDef to search */
+    Rect *area,			/* Area to search.  Edges coincident with the
 				 * right-hand side of this area are not seen;
 				 * they must lie to the left of area->r_xtop.
 				 */
-    TileTypeBitMask okTypes;
-    int (*proc)();		/* Function to apply at each edge */
-    ClientData cdata;		/* Additional argument to pass to (*proc)() */
+    const TileTypeBitMask *okTypesp,
+    int (*proc)(),		/* Function to apply at each edge */
+    ClientData cdata)		/* Additional argument to pass to (*proc)() */
 {
+    TileTypeBitMask okTypes = *okTypesp; /* TTMaskCopy(&okTypes, okTypesp) */
     Plane *plane = plowYankDef->cd_planes[pNum];
     struct shadow s;
     Tile *tp;
diff --git a/plow/PlowTest.c b/plow/PlowTest.c
index 999415df..75cf1bf1 100644
--- a/plow/PlowTest.c
+++ b/plow/PlowTest.c
@@ -240,7 +240,7 @@ PlowTest(w, cmd)
 	    saveDef = plowYankDef;
 	    plowYankDef = def;
 	    (void) plowSrShadow(PL_TECHDEPBASE, &editArea,
-			okTypes, plowShowShadow, (ClientData) def);
+			&okTypes, plowShowShadow, (ClientData) def);
 	    plowYankDef = saveDef;
 	    break;
 	case PC_TECHSHOW:
diff --git a/plow/plowInt.h b/plow/plowInt.h
index 996491cb..ea0afde7 100644
--- a/plow/plowInt.h
+++ b/plow/plowInt.h
@@ -264,7 +264,7 @@ extern void plowQueueDone();
 extern void plowQueueInit();
 extern int  plowSrFinalArea();
 extern void plowSrOutline(int pNum, Point *startPoint, const TileTypeBitMask *insideTypesp, int initialDir, int dirMask, int (*proc)(), ClientData cdata);
-extern int  plowSrShadow();
+extern int  plowSrShadow(int pNum, Rect *area, const TileTypeBitMask *okTypesp, int (*proc)(), ClientData cdata);
 extern int  plowSrShadowBack();
 extern int  plowSrShadowInitial();
 extern bool plowYankMore();