diff --git a/diff.c b/diff.c
index c14f69719b..d0be7c8f50 100644
--- a/diff.c
+++ b/diff.c
@@ -3606,8 +3606,8 @@ static int checkdiff_consume(void *priv, char *line, unsigned long len)
 }
 
 static unsigned char *deflate_it(char *data,
-				 unsigned long size,
-				 unsigned long *result_size)
+				 size_t size,
+				 size_t *result_size)
 {
 	size_t bound;
 	unsigned char *deflated;
@@ -3636,10 +3636,10 @@ static void emit_binary_diff_body(struct diff_options *o,
 	void *delta;
 	void *deflated;
 	void *data;
-	unsigned long orig_size;
-	unsigned long delta_size;
-	unsigned long deflate_size;
-	unsigned long data_size;
+	size_t orig_size;
+	size_t delta_size;
+	size_t deflate_size;
+	size_t data_size;
 
 	/* We could do deflated delta, or we could do just deflated two,
 	 * whichever is smaller.
@@ -3647,11 +3647,9 @@ static void emit_binary_diff_body(struct diff_options *o,
 	delta = NULL;
 	deflated = deflate_it(two->ptr, two->size, &deflate_size);
 	if (one->size && two->size) {
-		size_t delta_size_st = 0;
 		delta = diff_delta(one->ptr, one->size,
 				   two->ptr, two->size,
-				   &delta_size_st, deflate_size);
-		delta_size = cast_size_t_to_ulong(delta_size_st);
+				   &delta_size, deflate_size);
 		if (delta) {
 			void *to_free = delta;
 			orig_size = delta_size;