diff --git a/client/jansson/hashtable.c b/client/jansson/hashtable.c
index aee159242..071ba585f 100644
--- a/client/jansson/hashtable.c
+++ b/client/jansson/hashtable.c
@@ -222,7 +222,7 @@ int hashtable_set(hashtable_t *hashtable, const char *key, json_t *value) {
            allocated. */
 
         size_t len = strlen(key);
-        if (len >= (size_t) -1 - offsetof(pair_t, key)) {
+        if (len >= (size_t) - 1 - offsetof(pair_t, key)) {
             /* Avoid an overflow if the key is very long */
             return -1;
         }