diff --git a/core.c b/core.c
index 6e59993..8a1796f 100644
--- a/core.c
+++ b/core.c
@@ -105,7 +105,7 @@
 	return (void *)pkt->data + pkt->mctp_hdr_off + sizeof(struct mctp_hdr);
 }
 
-uint8_t mctp_pktbuf_size(struct mctp_pktbuf *pkt)
+size_t mctp_pktbuf_size(struct mctp_pktbuf *pkt)
 {
 	return pkt->end - pkt->start;
 }
diff --git a/libmctp.h b/libmctp.h
index 40e5371..a8beb72 100644
--- a/libmctp.h
+++ b/libmctp.h
@@ -55,7 +55,7 @@
 void mctp_pktbuf_free(struct mctp_pktbuf *pkt);
 struct mctp_hdr *mctp_pktbuf_hdr(struct mctp_pktbuf *pkt);
 void *mctp_pktbuf_data(struct mctp_pktbuf *pkt);
-uint8_t mctp_pktbuf_size(struct mctp_pktbuf *pkt);
+size_t mctp_pktbuf_size(struct mctp_pktbuf *pkt);
 void *mctp_pktbuf_alloc_start(struct mctp_pktbuf *pkt, size_t size);
 void *mctp_pktbuf_alloc_end(struct mctp_pktbuf *pkt, size_t size);
 int mctp_pktbuf_push(struct mctp_pktbuf *pkt, void *data, size_t len);