diff --git a/gtests/net/packetdrill/run_system_call.c b/gtests/net/packetdrill/run_system_call.c
index 0462434378419ecf09f3e23350931b278b0662bc..b9ec7f43017d65cd2a341a069f877b624e7ebc85 100644
--- a/gtests/net/packetdrill/run_system_call.c
+++ b/gtests/net/packetdrill/run_system_call.c
@@ -4456,8 +4456,8 @@ static int syscall_sendfile(struct state *state, struct syscall_spec *syscall,
 	if ((status == STATUS_OK) &&
 	    (script_sbytes != live_sbytes)) {
 		asprintf(error,
-			 "Expected sbytes %lu but got %lu",
-			 script_sbytes, live_sbytes);
+			 "Expected sbytes %lld but got %lld",
+			 (long long)script_sbytes, (long long)live_sbytes);
 		goto error_out;
 	}