diff --git a/config9.m4 b/config9.m4
index 8064df9..9782d18 100644
--- a/config9.m4
+++ b/config9.m4
@@ -68,6 +68,9 @@ if test "$PHP_PQ" != "no"; then
 	PQ_CHECK_CONST(PGRES_SINGLE_TUPLE)
 	PQ_CHECK_CONST(PGRES_COPY_BOTH)
 
+	PQ_CHECK_CONST(CONNECTION_CHECK_WRITABLE)
+	PQ_CHECK_CONST(CONNECTION_CONSUME)
+	PQ_CHECK_CONST(CONNECTION_GSS_STARTUP)
 
 	dnl
 	dnl PQ_CHECK_FUNC(sym, fail-hard)
diff --git a/src/php_pqconn.c b/src/php_pqconn.c
index fd5ec64..3a44a95 100644
--- a/src/php_pqconn.c
+++ b/src/php_pqconn.c
@@ -2139,6 +2139,15 @@ PHP_MINIT_FUNCTION(pqconn)
 	zend_declare_class_constant_long(php_pqconn_class_entry, ZEND_STRL("AUTH_OK"), CONNECTION_AUTH_OK);
 	zend_declare_class_constant_long(php_pqconn_class_entry, ZEND_STRL("SSL_STARTUP"), CONNECTION_SSL_STARTUP);
 	zend_declare_class_constant_long(php_pqconn_class_entry, ZEND_STRL("SETENV"), CONNECTION_SETENV);
+#ifdef HAVE_CONNECTION_CHECK_WRITABLE
+	zend_declare_class_constant_long(php_pqconn_class_entry, ZEND_STRL("CHECK_WRITABLE"), CONNECTION_CHECK_WRITABLE);
+#endif
+#ifdef HAVE_CONNECTION_CONSUME
+	zend_declare_class_constant_long(php_pqconn_class_entry, ZEND_STRL("CONSUME"), CONNECTION_CONSUME);
+#endif
+#ifdef HAVE_CONNECTION_GSS_STARTUP
+	zend_declare_class_constant_long(php_pqconn_class_entry, ZEND_STRL("GSS_STARTUP"), CONNECTION_GSS_STARTUP);
+#endif
 
 	zend_declare_class_constant_long(php_pqconn_class_entry, ZEND_STRL("TRANS_IDLE"), PQTRANS_IDLE);
 	zend_declare_class_constant_long(php_pqconn_class_entry, ZEND_STRL("TRANS_ACTIVE"), PQTRANS_ACTIVE);