diff --git a/ext2spice/ext2spice.c b/ext2spice/ext2spice.c
index 910ca773..9d6ee446 100644
--- a/ext2spice/ext2spice.c
+++ b/ext2spice/ext2spice.c
@@ -1122,7 +1122,7 @@ runexttospice:
 	if (flatFlags & EF_FLATCAPS)
 	    EFVisitCaps(spccapVisit, (ClientData) NULL);
 
-	EFVisitResists(spcresistVisit, (ClientData) NULL);
+	EFVisitResists(spcresistVisit, PTR2CD(NULL));
 	EFVisitSubcircuits(subcktVisit, (ClientData) NULL);
 
 	/* Visit nodes to find the substrate node */
@@ -1298,7 +1298,7 @@ main(
     if (flatFlags & EF_FLATCAPS)
 	EFVisitCaps(spccapVisit, (ClientData) NULL);
 
-    EFVisitResists(spcresistVisit, (ClientData) NULL);
+    EFVisitResists(spcresistVisit, PTR2CD(NULL));
     EFVisitSubcircuits(subcktVisit, (ClientData) NULL);
     esSpiceCapNode = StrDup((char **)NULL, esSpiceDefaultGnd);
     EFVisitNodes(spcnodeVisit, (ClientData) NULL);
@@ -3653,11 +3653,12 @@ spccapVisit(
  * ----------------------------------------------------------------------------
  */
 
+/* ARGSUSED */
 /* @typedef cb_extflat_visitresists_t (UNUSED) */
 int
 spcresistVisit(
-    HierName *hierName1,
-    HierName *hierName2,
+    const HierName *hierName1,
+    const HierName *hierName2,
     float res,
     ClientData cdata)	/* unused */
 {
diff --git a/ext2spice/ext2spice.h b/ext2spice/ext2spice.h
index 547b2b67..8eaba2f2 100644
--- a/ext2spice/ext2spice.h
+++ b/ext2spice/ext2spice.h
@@ -25,7 +25,7 @@ extern int spccapVisit(HierName *hierName1, HierName *hierName2, double cap, Cli
 extern int spcdevVisit(Dev *dev, HierContext *hc, float scale, Transform *trans, ClientData cdata); /* @typedef cb_extflat_visitdevs_t (UNUSED) */
 extern int spcnodeVisit(EFNode *node, int res, double cap, ClientData cdata); /* @typedef cb_extflat_visitnodes_t (UNUSED) */
 extern int subcktVisit(Use *use, HierName *hierName, bool is_top); /* @typedef cb_extflat_visitsubcircuits_t */
-extern int spcresistVisit(HierName *hierName1, HierName *hierName2, float res,  ClientData cdata); /* @typedef cb_extflat_visitresists_t (UNUSED) */
+extern int spcresistVisit(const HierName *hierName1, const HierName *hierName2, float res,  ClientData cdata); /* @typedef cb_extflat_visitresists_t (UNUSED) */
 extern int devMergeVisit(Dev *dev, HierContext *hc, float scale, Transform *trans, ClientData cdata); /* @typedef cb_extflat_visitdevs_t (UNUSED) */
 extern int devDistJunctVisit(Dev *dev, HierContext *hc, float scale, Transform *trans, ClientData cdata); /* @typedef cb_extflat_visitdevs_t (UNUSED) */
 extern int spcsubVisit(EFNode *node, int res, double cap, ClientData cdata); /* @typedef cb_extflat_visitnodes_t (char** resstr) */
diff --git a/extcheck/extcheck.c b/extcheck/extcheck.c
index e2760966..ba78530f 100644
--- a/extcheck/extcheck.c
+++ b/extcheck/extcheck.c
@@ -54,7 +54,7 @@ int ecNumNodeResists;
 int nodeVisit(EFNode *node, int res, double cap, ClientData cdata); /* @typedef cb_extflat_visitnodes_t (UNUSED) */
 int devVisit(Dev *dev, HierContext *hc, float scale, Transform *trans, ClientData cdata); /* @typedef cb_extflat_visitdevs_t (UNUSED) */
 int capVisit(HierName *hn1, HierName *hn2, double cap, ClientData cdata); /* @typedef cb_extflat_visitcaps_t (UNUSED) */
-int resistVisit(HierName *hn1, HierName *hn2, float res, ClientData cdata); /* @typedef cb_extflat_visitresists_t (UNUSED) */
+int resistVisit(const HierName *hn1, const HierName *hn2, float res, ClientData cdata); /* @typedef cb_extflat_visitresists_t (UNUSED) */
 
 /*
  * ----------------------------------------------------------------------------
@@ -89,7 +89,7 @@ main(int argc, char *argv[])
     if (IS_FINITE_F(EFCapThreshold))
 	EFVisitCaps(capVisit, (ClientData) NULL);
     if (EFResistThreshold != INFINITE_THRESHOLD)
-	EFVisitResists(resistVisit, (ClientData) NULL);
+	EFVisitResists(resistVisit, PTR2CD(NULL));
     EFVisitNodes(nodeVisit, (ClientData) NULL);
 
 #ifdef	free_all_mem
@@ -181,8 +181,8 @@ capVisit(
 /* @typedef cb_extflat_visitresists_t (UNUSED) */
 int
 resistVisit(
-    HierName *hn1,
-    HierName *hn2,	/* UNUSED */
+    const HierName *hn1,
+    const HierName *hn2,/* UNUSED */
     float res,
     ClientData cdata)   /* UNUSED */
 {
diff --git a/extflat/EFvisit.c b/extflat/EFvisit.c
index 87e28f8f..b8a831b2 100644
--- a/extflat/EFvisit.c
+++ b/extflat/EFvisit.c
@@ -456,12 +456,14 @@ skip:
  * Must be called after EFFlatBuild().
  * For each resistor in the circuit, call the user-supplied procedure
  * (*resProc)(), which should be of the following form, where hn1 and
- * hn2 are the HierNames of the two nodes connected by the resistor.
+ * hn2 are the HierNames of the two nodes connected by the resistor
+ *   see also typedef cb_extflat_visitresists_t:
  *
- *	(*resProc)(hn1, hn2, resistance, cdata)
- *	    HierName *hn1, *hn2;
- *	    int resistance;
- *	    ClientData cdata;
+ *	int (*resProc)(
+ *	    const HierName *hn1,
+ *	    const HierName *hn2,
+ *	    float resistance,
+ *	    ClientData cdata)
  *	{
  *	}
  *
@@ -482,15 +484,15 @@ skip:
  */
 
 int
-EFVisitResists(resProc, cdata)
-    int (*resProc)();
-    ClientData cdata;
+EFVisitResists(
+    const cb_extflat_visitresists_t resProc,
+    ClientData cdata)
 {
     CallArg ca;
 
-    ca.ca_proc = resProc;
+    ca.ca_proc = (int (*)()) resProc;
     ca.ca_cdata = cdata;
-    return efVisitResists(&efFlatContext, (ClientData) &ca);
+    return efVisitResists(&efFlatContext, &ca);
 }
 
 /*
@@ -585,7 +587,7 @@ efVisitSingleResist(hc, name1, name2, res, ca)
 
     return (*ca->ca_proc)(n1->efnode_name->efnn_hier,
 		n2->efnode_name->efnn_hier,
-		res->conn_res, ca->ca_cdata);
+		res->conn_res, ca->ca_cdata); /* @invoke cb_extflat_visitresists_t */
 }
 
 /*
diff --git a/extflat/extflat.h b/extflat/extflat.h
index 52270cc7..6fd3ac81 100644
--- a/extflat/extflat.h
+++ b/extflat/extflat.h
@@ -118,8 +118,9 @@ typedef int (*cb_extflat_visitdevs_t)(Dev *dev, HierContext *hc, float scale, Tr
 extern int EFVisitDevs(const cb_extflat_visitdevs_t devProc, ClientData cdata);
 extern int efVisitDevs(HierContext *hc, CallArg *ca);
 extern bool efSymLook();
-extern int  efVisitResists();
-extern int  EFVisitResists();
+extern int efVisitResists(HierContext *hc, CallArg *ca);
+typedef int (*cb_extflat_visitresists_t)(const HierName *hn1, const HierName *hn2, float resistance, ClientData cdata);
+extern int EFVisitResists(const cb_extflat_visitresists_t resProc, ClientData cdata);
 extern int  EFVisitNodes();
 extern int  EFVisitCaps();
 extern void EFGetLengthAndWidth();