diff --git a/ext2sim/ext2sim.c b/ext2sim/ext2sim.c
index dd183033..ad6ece6b 100644
--- a/ext2sim/ext2sim.c
+++ b/ext2sim/ext2sim.c
@@ -1581,7 +1581,7 @@ simresistVisit(
     const HierName *hierName1,
     const HierName *hierName2,
     float res,
-    ClientData)	/* unused */
+    ClientData cdata)	/* unused */
 {
     fprintf(esSimF, "r ");
     EFHNOut(hierName1, esSimF);