diff --git a/kitty/disk-cache.c b/kitty/disk-cache.c
index 5c7f43edc..33d5ee0f3 100644
--- a/kitty/disk-cache.c
+++ b/kitty/disk-cache.c
@@ -85,7 +85,7 @@ static int
 open_cache_file_without_tmpfile(const char *cache_path) {
     int fd = -1;
     static const char *template = "%s/disk-cache-XXXXXXXXXXXX";
-    size_t sz = strlen(cache_path) + sizeof(template);
+    const size_t sz = strlen(cache_path) + sizeof(template) + 4;
     FREE_AFTER_FUNCTION char *buf = calloc(1, sz);
     if (!buf) { errno = ENOMEM; return -1; }
     snprintf(buf, sz - 1, template, cache_path);