diff --git a/ui-patch.c b/ui-patch.c
index 8007a11..82f125b 100644
--- a/ui-patch.c
+++ b/ui-patch.c
@@ -11,13 +11,16 @@
 #include "html.h"
 #include "ui-shared.h"
 
+/* two commit hashes with two dots in between and termination */
+#define REV_RANGE_LEN 2 * GIT_MAX_HEXSZ + 3
+
 void cgit_print_patch(const char *new_rev, const char *old_rev,
 		      const char *prefix)
 {
 	struct rev_info rev;
 	struct commit *commit;
 	struct object_id new_rev_oid, old_rev_oid;
-	char rev_range[2 * 40 + 3];
+	char rev_range[REV_RANGE_LEN];
 	const char *rev_argv[] = { NULL, "--reverse", "--format=email", rev_range, "--", prefix, NULL };
 	int rev_argc = ARRAY_SIZE(rev_argv) - 1;
 	char *patchname;
@@ -60,7 +63,7 @@ void cgit_print_patch(const char *new_rev, const char *old_rev,
 	if (is_null_oid(&old_rev_oid)) {
 		memcpy(rev_range, oid_to_hex(&new_rev_oid), GIT_SHA1_HEXSZ + 1);
 	} else {
-		sprintf(rev_range, "%s..%s", oid_to_hex(&old_rev_oid),
+		xsnprintf(rev_range, REV_RANGE_LEN, "%s..%s", oid_to_hex(&old_rev_oid),
 			oid_to_hex(&new_rev_oid));
 	}