--- a/src/interfaces/libpq/libpq-fe.h
+++ b/src/interfaces/libpq/libpq-fe.h
@@ -321,16 +328,28 @@ extern PostgresPollingStatusType PQresetPoll(PGconn *conn);
 /* Synchronous (blocking) */
 extern void PQreset(PGconn *conn);
 
+/* issue a cancel request */
+extern PGcancelConn * PQcancelSend(PGconn *conn);