diff --git a/src/pv/transfer.c b/src/pv/transfer.c
index 61af8d4..4b390d7 100644
--- a/src/pv/transfer.c
+++ b/src/pv/transfer.c
@@ -686,7 +686,11 @@ static int pv__transfer_write(pvstate_t state, bool *eof_in, bool *eof_out, long
 						       state->transfer.write_position,
 						       (size_t) (state->transfer.to_write),
 						       state->control.sync_after_write);
-		debug("%s: %ld", "bytes written", (long) nwritten);
+		if (nwritten < 0) {
+			debug("%s: %ld: %s", "bytes written", (long) nwritten, strerror(errno));
+		} else {
+			debug("%s: %ld", "bytes written", (long) nwritten);
+		}
 #if HAVE_SETITIMER
 		memset(&new_timer, 0, sizeof(new_timer));
 		new_timer.it_interval.tv_sec = 0;