diff --git a/src/flb_utils.c b/src/flb_utils.c
index 659411619ee..1fcd472e9ef 100644
--- a/src/flb_utils.c
+++ b/src/flb_utils.c
@@ -812,8 +812,8 @@ int flb_utils_time_split(const char *time, int *sec, long *nsec)
 void flb_utils_bytes_to_human_readable_size(size_t bytes,
                                             char *out_buf, size_t size)
 {
-    unsigned long i;
-    unsigned long u = 1024;
+    uint64_t i;
+    uint64_t u = 1024;
     static const char *__units[] = {
         "b", "K", "M", "G",
         "T", "P", "E", "Z", "Y", NULL