diff --git a/json_util.c b/json_util.c
index 1a2dfcd..0f570f2 100644
--- a/json_util.c
+++ b/json_util.c
@@ -269,7 +269,12 @@ int json_parse_uint64(const char *buf, uint64_t *retval)
 	val = strtoull(buf, &end, 10);
 	if (end != buf)
 		*retval = val;
-	return ((val == 0 && errno != 0) || (end == buf)) ? 1 : 0;
+	if ((val == 0 && errno != 0) || (end == buf))
+	{
+		errno = EINVAL;
+		return 1;
+	}
+	return 0;
 }
 
 #ifndef HAVE_REALLOC
diff --git a/json_util.h b/json_util.h
index 1f663e8..62ad688 100644
--- a/json_util.h
+++ b/json_util.h
@@ -100,8 +100,17 @@ JSON_EXPORT int json_object_to_fd(int fd, struct json_object *obj, int flags);
  */
 JSON_EXPORT const char *json_util_get_last_err(void);
 
-/* these parsing helpers return zero on success */
+/**
+ * A parsing helper for integer values.  Returns 0 on success,
+ * with the parsed value assigned to *retval.  Overflow/underflow
+ * are NOT considered errors, but errno will be set to ERANGE,
+ * just like the strtol/strtoll functions do.
+ */
 JSON_EXPORT int json_parse_int64(const char *buf, int64_t *retval);
+/**
+ * A parsing help for integer values, providing one extra bit of 
+ * magnitude beyond json_parse_int64().
+ */
 JSON_EXPORT int json_parse_uint64(const char *buf, uint64_t *retval);
 /**
  * @deprecated