diff --git a/src/shared/hibernate-util.c b/src/shared/hibernate-util.c
index c6c58f8e5d..97568aae68 100644
--- a/src/shared/hibernate-util.c
+++ b/src/shared/hibernate-util.c
@@ -390,6 +390,9 @@ int read_fiemap(int fd, struct fiemap **ret) {
         uint64_t fiemap_start = 0, fiemap_length;
         const size_t n_extra = DIV_ROUND_UP(sizeof(struct fiemap), sizeof(struct fiemap_extent));
 
+        assert(fd >= 0);
+        assert(ret);
+
         if (fstat(fd, &statinfo) < 0)
                 return log_debug_errno(errno, "Cannot determine file size: %m");
         if (!S_ISREG(statinfo.st_mode))