diff --git a/include/prototypes.h b/include/prototypes.h
index c9825c45..ad63a63f 100644
--- a/include/prototypes.h
+++ b/include/prototypes.h
@@ -556,7 +556,7 @@ extern void pln_dropoff(struct emp_qelem *, struct ichrstr *,
 extern void pln_mine(struct emp_qelem *list, struct sctstr *sectp);
 extern void pln_sel(struct nstr_item *, struct emp_qelem *,
 		    struct sctstr *, int, int, int, int);
-extern int pln_arm(struct emp_qelem *, int, int, struct ichrstr *,
+extern int pln_arm(struct emp_qelem *, int, char, struct ichrstr *,
 		   int, int);
 extern int pln_mobcost(int, struct plnstr *, int);
 extern void pln_put(struct emp_qelem *);
diff --git a/src/lib/subs/plnsub.c b/src/lib/subs/plnsub.c
index eab65fca..d6a6cb24 100644
--- a/src/lib/subs/plnsub.c
+++ b/src/lib/subs/plnsub.c
@@ -561,7 +561,7 @@ pln_sel(struct nstr_item *ni, struct emp_qelem *list, struct sctstr *ap,
 }
 
 int
-pln_arm(struct emp_qelem *list, int dist, int mission, struct ichrstr *ip,
+pln_arm(struct emp_qelem *list, int dist, char mission, struct ichrstr *ip,
 	int flags, int mission_flags)
 {
     struct emp_qelem *qp;