diff --git a/lib/roken/roken.h b/lib/roken/roken.h
index 5f522767f..5c07132f8 100644
--- a/lib/roken/roken.h
+++ b/lib/roken/roken.h
@@ -52,7 +52,7 @@ void herror(char *s);
 #ifndef HAVE_INET_ATON
 /* Minimal implementation of inet_aton. Doesn't handle hex numbers. */
 #ifndef __GNUC__
-int inet_aton(char *cp, struct in_addr *adr);
+int inet_aton(const char *cp, struct in_addr *adr);
 #endif
 #endif
 
diff --git a/lib/roken/roken.h.in b/lib/roken/roken.h.in
index 5f522767f..5c07132f8 100644
--- a/lib/roken/roken.h.in
+++ b/lib/roken/roken.h.in
@@ -52,7 +52,7 @@ void herror(char *s);
 #ifndef HAVE_INET_ATON
 /* Minimal implementation of inet_aton. Doesn't handle hex numbers. */
 #ifndef __GNUC__
-int inet_aton(char *cp, struct in_addr *adr);
+int inet_aton(const char *cp, struct in_addr *adr);
 #endif
 #endif