diff --git a/utils.c b/utils.c
index d2410444..5bedd97f 100644
--- a/utils.c
+++ b/utils.c
@@ -1213,7 +1213,7 @@ out:
 }
 
 static char *size_strs[] = { "", "KiB", "MiB", "GiB", "TiB", "PiB", "EiB"};
-int pretty_size_snprintf(double size, char *str, size_t str_bytes)
+int pretty_size_snprintf(u64 size, char *str, size_t str_bytes)
 {
 	int num_divs = 0;
 	float fraction;
diff --git a/utils.h b/utils.h
index 4d0db1dc..6f4b10c1 100644
--- a/utils.h
+++ b/utils.h
@@ -57,7 +57,7 @@ int check_mounted_where(int fd, const char *file, char *where, int size,
 int btrfs_device_already_in_root(struct btrfs_root *root, int fd,
 				 int super_offset);
 
-int pretty_size_snprintf(double size, char *str, size_t str_bytes);
+int pretty_size_snprintf(u64 size, char *str, size_t str_bytes);
 #define pretty_size(size) 						\
 	({								\
 		static __thread char _str[24];				\