diff --git a/tr-bridge.c b/tr-bridge.c
index 72efabb..59f5a3c 100644
--- a/tr-bridge.c
+++ b/tr-bridge.c
@@ -196,7 +196,7 @@ static int eth2tr(struct bridge_state *bst)
 	/* 802.3 frame: 'proto' is actually the length */
 	eth_payload_len = htons(ethh->h_proto);
 	if (sizeof(*ethh) + eth_payload_len > ethlen) {
-		fprintf(stderr, "TR<-ETH: Not bridging unrealistically long (%lu > %u) frame %s->%s\n",
+		fprintf(stderr, "TR<-ETH: Not bridging unrealistically long (%zu > %u) frame %s->%s\n",
 			sizeof(*ethh) + eth_payload_len, ethlen, eth_src, eth_dst);
 		return 0;
 	}