diff --git a/range-diff.c b/range-diff.c
index f64e84f56a..9e2b788cdf 100644
--- a/range-diff.c
+++ b/range-diff.c
@@ -37,7 +37,7 @@ static int read_patches(const char *range, struct string_list *list,
 	struct patch_util *util = NULL;
 	int in_header = 1;
 	char *line, *current_filename = NULL;
-	int len;
+	ssize_t len;
 	size_t size;
 
 	strvec_pushl(&cp.args, "log", "--no-color", "-p", "--no-merges",