diff --git a/src/frontend/numparam/xpressn.c b/src/frontend/numparam/xpressn.c
index 010dfc1e0..352dc7e7e 100644
--- a/src/frontend/numparam/xpressn.c
+++ b/src/frontend/numparam/xpressn.c
@@ -1187,7 +1187,7 @@ insertnumber(dico_t *dico, int i, char *s, SPICE_DSTRINGPTR ustr_p)
 
 
 bool
-nupa_substitute(dico_t *dico, char * const s, char *r)
+nupa_substitute(dico_t *dico, char * const s_, char *r)
 /* s: pointer to original source line.
    r: pointer to result line, already heavily modified wrt s
    anywhere we find a 10-char numstring in r, substitute it.
@@ -1204,8 +1204,8 @@ nupa_substitute(dico_t *dico, char * const s, char *r)
     spice_dstring_init(&qstr);
     spice_dstring_init(&tstr);
     const char *iptr;
-    iptr = s;
-    const char * const s_end = strchr(s, '\0');
+    iptr = s_;
+    const char * const s_end = strchr(s_, '\0');
     const char *kptr;
 
     while ((iptr < s_end) && !err) {