diff --git a/src/misc/string.c b/src/misc/string.c
index 14d049514..19cecec10 100644
--- a/src/misc/string.c
+++ b/src/misc/string.c
@@ -319,6 +319,8 @@ gettok(char **s)
 char *
 nexttok(const char *s)
 {
+    if (!s)
+        return NULL;
     int paren = 0;
 
     s = skip_ws(s);