diff --git a/json_tokener.c b/json_tokener.c
index 773229e..1954bcd 100644
--- a/json_tokener.c
+++ b/json_tokener.c
@@ -154,6 +154,9 @@ struct json_tokener *json_tokener_new_ex(int depth)
 {
 	struct json_tokener *tok;
 
+	if (depth < 1)
+		return NULL;
+
 	tok = (struct json_tokener *)calloc(1, sizeof(struct json_tokener));
 	if (!tok)
 		return NULL;
diff --git a/json_tokener.h b/json_tokener.h
index 54925e5..f53a761 100644
--- a/json_tokener.h
+++ b/json_tokener.h
@@ -206,6 +206,7 @@ JSON_EXPORT struct json_tokener *json_tokener_new(void);
 
 /**
  * Allocate a new json_tokener with a custom max nesting depth.
+ * The depth must be at least 1.
  * @see JSON_TOKENER_DEFAULT_DEPTH
  */
 JSON_EXPORT struct json_tokener *json_tokener_new_ex(int depth);