diff --git a/extract/ExtMain.c b/extract/ExtMain.c
index eac2b5ee..3307034d 100644
--- a/extract/ExtMain.c
+++ b/extract/ExtMain.c
@@ -806,11 +806,11 @@ extContainsGeometry(def, allButUse, area)
     Rect *area;
 {
     int extContainsPaintFunc();
-    bool extContainsCellFunc();
+    int extContainsCellFunc(CellUse *use, ClientData cdata); /* cb_database_srcellplanearea_t (const CellUse *allButUse) */
     int pNum;
 
     if (DBSrCellPlaneArea(def->cd_cellPlane, area,
-			extContainsCellFunc, (ClientData) allButUse))
+			extContainsCellFunc, PTR2CD(allButUse)))
 	return (TRUE);
 
     for (pNum = PL_TECHDEPBASE; pNum < DBNumPlanes; pNum++)
@@ -824,11 +824,13 @@ extContainsGeometry(def, allButUse, area)
 
 /* ------------------------------------------------------------------------- */
 
-bool
-extContainsCellFunc(use, allButUse)
-    CellUse *use;
-    CellUse *allButUse;
+/** @typedef cb_database_srcellplanearea_t */
+int
+extContainsCellFunc(
+    CellUse *use,
+    ClientData cdata)
 {
+    const CellUse *allButUse = (CellUse *)CD2PTR(cdata);
     return (use != allButUse) ? TRUE : FALSE;
 }