diff --git a/VERSION b/VERSION
index 24ae6434..f9f294c7 100644
--- a/VERSION
+++ b/VERSION
@@ -1 +1 @@
-8.3.636
+8.3.637
diff --git a/drc/DRCbasic.c b/drc/DRCbasic.c
index f548be34..d23dbe81 100644
--- a/drc/DRCbasic.c
+++ b/drc/DRCbasic.c
@@ -524,6 +524,13 @@ DRCBasicCheck (celldef, checkRect, clipRect, function, cdata)
     return (errors);
 }
 
+/* Expect that keeping around 3 MaxRectsData records should be sufficient
+ * to avoid recomputing drcCanonicalMaxwidth() multiple times.  Note that
+ * if a PDK sets up multiple rules on an edge which all require running
+ * drcCanonicalMaxwidth(), then this cache size may need to be revisited.
+ */
+#define MAXRECTSCACHE 3
+
 /*
  * ----------------------------------------------------------------------------
  *
@@ -561,6 +568,19 @@ drcTile (tile, dinfo, arg)
     int triggered;
     int cdist, dist, ccdist, result;
 
+    /* Keep up to three MaxRectsData records to avoid doing the	same
+     * expensive computation more than once.
+     *
+     * mrdcache[0] will be used for the tpleft tile, since it will never
+     * be reused.  mrdcache[1] and mrdcache[2] will be used for the tile
+     * itself.  Note that if more than 2 DRCCookie entries for the same
+     * edge require drcCanonicalMaxwidth(), then mrdcache[2] will be
+     * re-used so that at least mrdcache[1] is always a cache hit.
+     */
+
+    static MaxRectsData *mrdcache[MAXRECTSCACHE] = {NULL, NULL, NULL};
+    DRCCookie *cptrcache;
+
     arg->dCD_constraint = &errRect;
 
     /*
@@ -702,6 +722,8 @@ drcTile (tile, dinfo, arg)
 	DRCstatEdges++;
     }
 
+    cptrcache = NULL;
+
     /*
      * Check design rules along a vertical boundary between two tiles.
      *
@@ -857,12 +879,23 @@ drcTile (tile, dinfo, arg)
 
 		    if (cptr->drcc_flags & DRC_REVERSE)
 		    {
-			mrd = drcCanonicalMaxwidth(tpleft, GEO_WEST, arg, cptr);
+			mrd = drcCanonicalMaxwidth(tpleft, GEO_WEST, arg, cptr,
+					&mrdcache[0]);
 			triggered = 0;
 		    }
-		    else if (firsttile)
+		    else
 		    {
-			mrd = drcCanonicalMaxwidth(tile, GEO_EAST, arg, cptr);
+			if (cptrcache == NULL)
+			{
+			    mrd = drcCanonicalMaxwidth(tile, GEO_EAST, arg, cptr,
+					&mrdcache[1]);
+			    cptrcache = cptr;
+			}
+			else if (cptrcache != cptr)
+			    mrd = drcCanonicalMaxwidth(tile, GEO_EAST, arg, cptr,
+					&mrdcache[2]);
+			else
+			    mrd = mrdcache[1];
 			triggered = 0;
 		    }
 		    if (!trigpending || (DRCCurStyle->DRCFlags
@@ -1153,6 +1186,8 @@ drcTile (tile, dinfo, arg)
         }
     }
 
+    cptrcache = NULL;
+
     /*
      * Check design rules along a horizontal boundary between two tiles.
      *
@@ -1299,12 +1334,23 @@ drcTile (tile, dinfo, arg)
 
 		    if (cptr->drcc_flags & DRC_REVERSE)
 		    {
-			mrd = drcCanonicalMaxwidth(tpbot, GEO_SOUTH, arg, cptr);
+			mrd = drcCanonicalMaxwidth(tpbot, GEO_SOUTH, arg, cptr,
+					&mrdcache[0]);
 			triggered = 0;
 		    }
-		    else if (firsttile)
+		    else
 		    {
-			mrd = drcCanonicalMaxwidth(tile, GEO_NORTH, arg, cptr);
+			if (cptrcache == NULL)
+			{
+			    mrd = drcCanonicalMaxwidth(tile, GEO_NORTH, arg, cptr,
+					&mrdcache[1]);
+			    cptrcache = cptr;
+			}
+			else if (cptrcache != cptr)
+			    mrd = drcCanonicalMaxwidth(tile, GEO_NORTH, arg, cptr,
+					&mrdcache[2]);
+			else
+			    mrd = mrdcache[1];
 			triggered = 0;
 		    }
 		    if (!trigpending || (DRCCurStyle->DRCFlags
diff --git a/drc/DRCextend.c b/drc/DRCextend.c
index 5855babb..6162070a 100644
--- a/drc/DRCextend.c
+++ b/drc/DRCextend.c
@@ -510,16 +510,17 @@ MaxRectsExclude(
  */
 
 MaxRectsData *
-drcCanonicalMaxwidth(starttile, dir, arg, cptr)
+drcCanonicalMaxwidth(starttile, dir, arg, cptr, mrdptr)
     Tile	*starttile;
     int		dir;			/* direction of rule */
     struct	drcClientData	*arg;
     DRCCookie	*cptr;
+    MaxRectsData **mrdptr;
 {
     int		    s, edgelimit;
     Tile	    *tile,*tp;
     TileTypeBitMask wrongtypes;
-    static MaxRectsData *mrd = (MaxRectsData *)NULL;
+    MaxRectsData    *mrd = *mrdptr;
     Rect	    *boundrect, boundorig;
 
     /* Generate an initial array size of 8 for rlist and swap. */
@@ -529,6 +530,7 @@ drcCanonicalMaxwidth(starttile, dir, arg, cptr)
 	mrd->rlist = (Rect *)mallocMagic(8 * sizeof(Rect));
 	mrd->swap = (Rect *)mallocMagic(8 * sizeof(Rect));
 	mrd->listdepth = 8;
+	*mrdptr = mrd;
     }
     if (starttile == NULL) return mrd;