diff --git a/src/php_pqconn.c b/src/php_pqconn.c
index dd08ced..4baa5ec 100644
--- a/src/php_pqconn.c
+++ b/src/php_pqconn.c
@@ -1621,7 +1621,7 @@ STATUS php_pqconn_start_transaction(zval *zconn, php_pqconn_object_t *conn_obj,
 	} else {
 		PGresult *res;
 		smart_str cmd = {0};
-		const char *il = isolation_level(&isolation);
+		const char *il = php_pq_isolation_level(&isolation);
 
 		smart_str_appends(&cmd, "START TRANSACTION ISOLATION LEVEL ");
 		smart_str_appends(&cmd, il);
@@ -1660,7 +1660,7 @@ STATUS php_pqconn_start_transaction_async(zval *zconn, php_pqconn_object_t *conn
 		throw_exce(EX_UNINITIALIZED TSRMLS_CC, "pq\\Connection not initialized");
 	} else {
 		smart_str cmd = {0};
-		const char *il = isolation_level(&isolation);
+		const char *il = php_pq_isolation_level(&isolation);
 
 		smart_str_appends(&cmd, "START TRANSACTION ISOLATION LEVEL ");
 		smart_str_appends(&cmd, il);
diff --git a/src/php_pqtxn.h b/src/php_pqtxn.h
index 920e570..0c8fd86 100644
--- a/src/php_pqtxn.h
+++ b/src/php_pqtxn.h
@@ -38,7 +38,7 @@ typedef struct php_pqtxn_object {
 	php_pqtxn_t *intern;
 } php_pqtxn_object_t;
 
-extern const char *isolation_level(long *isolation);
+extern const char *php_pq_isolation_level(long *isolation);
 
 extern zend_class_entry *php_pqtxn_class_entry;
 extern zend_object_value php_pqtxn_create_object_ex(zend_class_entry *ce, php_pqtxn_t *intern, php_pqtxn_object_t **ptr TSRMLS_DC);