diff --git a/drc/DRCcontin.c b/drc/DRCcontin.c
index 000050a7..2af43e8d 100644
--- a/drc/DRCcontin.c
+++ b/drc/DRCcontin.c
@@ -615,6 +615,7 @@ drcCheckTile(tile, arg)
     Rect erasebox;		/* erase old ERROR tiles in this
 				 * region and clip new ERRORs to it
 				 */
+    Rect checkbox;
     CellDef * celldef;		/* First CellDef on DRCPending list. */
     Rect redisplayArea;		/* Area to be redisplayed. */
     extern int drcXorFunc();	/* Forward declarations. */
@@ -644,6 +645,12 @@ drcCheckTile(tile, arg)
 	erasebox.r_xtop, erasebox.r_ytop);
     */
 
+    /* checkbox is erasebox expanded by DRCTechHalo.  Note that this is	*/
+    /* computed independently inside DRCInteractionCheck().		*/
+
+    GEO_EXPAND(&erasebox, DRCTechHalo, &checkbox);
+    GeoClip(&checkbox, &square);
+
     /* Use drcDisplayPlane to save all the current errors in the
      * area we're about to recheck.
      */
@@ -675,8 +682,8 @@ drcCheckTile(tile, arg)
      */
 
     DRCErrorType = TT_ERROR_S;
-    (void) DRCInteractionCheck(celldef, &erasebox, drcPaintError,
-		(ClientData) drcTempPlane);
+    (void) DRCInteractionCheck(celldef, &square, &erasebox,
+		drcPaintError, (ClientData) drcTempPlane);
     
     /* Check #3:  check for array formation errors in the area. */
 
@@ -700,10 +707,10 @@ drcCheckTile(tile, arg)
     DBPaintPlane(celldef->cd_planes[PL_DRC_CHECK], &erasebox,
 	DBStdEraseTbl(TiGetType(tile), PL_DRC_CHECK),
 	(PaintUndoInfo *) NULL);
-    DBPaintPlane(celldef->cd_planes[PL_DRC_ERROR], &erasebox,
+    DBPaintPlane(celldef->cd_planes[PL_DRC_ERROR], &checkbox,
 	DBStdEraseTbl(TT_ERROR_P, PL_DRC_ERROR),
 	(PaintUndoInfo *) NULL);
-    DBPaintPlane(celldef->cd_planes[PL_DRC_ERROR], &square,
+    DBPaintPlane(celldef->cd_planes[PL_DRC_ERROR], &checkbox,
 	DBStdEraseTbl(TT_ERROR_S, PL_DRC_ERROR),
 	(PaintUndoInfo *) NULL);
     (void) DBSrPaintArea((Tile *) NULL, drcTempPlane, &TiPlaneRect,
diff --git a/drc/DRCmain.c b/drc/DRCmain.c
index ed119de7..a9c879f0 100644
--- a/drc/DRCmain.c
+++ b/drc/DRCmain.c
@@ -530,7 +530,7 @@ drcWhyFunc(scx, cdarg)
 
     /* Check paint and interactions in this subcell. */
     
-    (void) DRCInteractionCheck(def, &scx->scx_area,
+    (void) DRCInteractionCheck(def, &scx->scx_area, &scx->scx_area,
 		(dolist) ? drcListError : drcPrintError,
 		(ClientData) scx);
     (void) DRCArrayCheck(def, &scx->scx_area,
@@ -554,7 +554,7 @@ drcWhyAllFunc(scx, cdarg)
 
     /* Check paint and interactions in this subcell. */
     
-    (void) DRCInteractionCheck(def, &scx->scx_area,
+    (void) DRCInteractionCheck(def, &scx->scx_area, &scx->scx_area,
 		drcListallError, (ClientData)scx);
     (void) DRCArrayCheck(def, &scx->scx_area,
 		drcListallError, (ClientData)scx);
diff --git a/drc/DRCsubcell.c b/drc/DRCsubcell.c
index 561845ad..53eca616 100644
--- a/drc/DRCsubcell.c
+++ b/drc/DRCsubcell.c
@@ -573,8 +573,9 @@ drcExactOverlapTile(tile, cxp)
  */
 
 int
-DRCInteractionCheck(def, erasebox, func, cdarg)
+DRCInteractionCheck(def, area, erasebox, func, cdarg)
     CellDef *def;		/* Definition in which to do check. */
+    Rect *area;			/* Area in which all errors are to be found. */
     Rect *erasebox;		/* Smaller area containing DRC check tiles */
     void (*func)();		/* Function to call for each error. */
     ClientData cdarg;		/* Extra info to be passed to func. */
@@ -595,13 +596,13 @@ DRCInteractionCheck(def, erasebox, func, cdarg)
      * square separately.
      */
     
-    x = (erasebox->r_xbot/DRCStepSize) * DRCStepSize;
-    if (x > erasebox->r_xbot) x -= DRCStepSize;
-    y = (erasebox->r_ybot/DRCStepSize) * DRCStepSize;
-    if (y > erasebox->r_ybot) y -= DRCStepSize;
-    for (square.r_xbot = x; square.r_xbot < erasebox->r_xtop;
+    x = (area->r_xbot/DRCStepSize) * DRCStepSize;
+    if (x > area->r_xbot) x -= DRCStepSize;
+    y = (area->r_ybot/DRCStepSize) * DRCStepSize;
+    if (y > area->r_ybot) y -= DRCStepSize;
+    for (square.r_xbot = x; square.r_xbot < area->r_xtop;
 	 square.r_xbot += DRCStepSize)
-	for (square.r_ybot = y; square.r_ybot < erasebox->r_ytop;
+	for (square.r_ybot = y; square.r_ybot < area->r_ytop;
 	     square.r_ybot += DRCStepSize)
 	{
 	    square.r_xtop = square.r_xbot + DRCStepSize;
@@ -613,7 +614,7 @@ DRCInteractionCheck(def, erasebox, func, cdarg)
 	    /* large step size.						*/
 
             cliparea = square;
-	    GeoClip(&cliparea, erasebox);
+	    GeoClip(&cliparea, area);
 
 	    /* Find all the interactions in the square, and clip to the error
 	     * area we're interested in. */
@@ -621,7 +622,7 @@ DRCInteractionCheck(def, erasebox, func, cdarg)
 	    if (!DRCFindInteractions(def, &cliparea, DRCTechHalo, &intArea))
 	    {
 		/* Added May 4, 2008---if there are no subcells, run the
-		 * basic check over the area of the square.
+		 * basic check over the area of the erasebox.
 		 */
 		subArea = *erasebox;
 		GeoClip(&subArea, &cliparea);
@@ -691,6 +692,12 @@ DRCInteractionCheck(def, erasebox, func, cdarg)
 		}
 		DRCErrorType = errorSaveType;
 	    }
+
+ 	    /* Clip interaction area against subArea-expanded-by-halo */
+
+	    subArea = *erasebox;
+	    GEO_EXPAND(&subArea, DRCTechHalo, &cliparea);
+	    GeoClip(&intArea, &cliparea);
     
 	    /* Flatten the interaction area. */