diff --git a/ext/session/session.c b/ext/session/session.c
index d652383b4560..1fa9319fcfac 100644
--- a/ext/session/session.c
+++ b/ext/session/session.c
@@ -2031,7 +2031,7 @@ static PHP_FUNCTION(session_set_save_handler)
 			remove_user_shutdown_function("session_shutdown", sizeof("session_shutdown") - 1);
 		}
 
-		if (PS(mod) && PS(session_status) != php_session_active && PS(mod) != &ps_mod_user) {
+		if (PS(session_status) != php_session_active && (!PS(mod) || PS(mod) != &ps_mod_user)) {
 			ini_name = zend_string_init("session.save_handler", sizeof("session.save_handler") - 1, 0);
 			ini_val = zend_string_init("user", sizeof("user") - 1, 0);
 			PS(set_handler) = 1;
diff --git a/ext/session/tests/bug80889.phpt b/ext/session/tests/bug80889.phpt
new file mode 100644
index 000000000000..78e1a6ab64b4
--- /dev/null
+++ b/ext/session/tests/bug80889.phpt
@@ -0,0 +1,37 @@
+--TEST--
+Bug #80889 (Cannot set save handler when save_handler is invalid)
+--SKIPIF--
+<?php include('skipif.inc'); ?>
+--INI--
+session.save_handler=whatever
+--FILE--
+<?php
+class DummyHandler implements SessionHandlerInterface {
+    public function open($savePath, $sessionName) {
+        return true;
+    }
+    public function close() {
+        return true;
+    }
+    public function read($id) {
+        return '';
+    }
+    public function write($id, $data) {
+        return true;
+    }
+    public function destroy($id) {
+        return true;
+    }
+    public function gc($maxlifetime) {
+        return true;
+    }
+}
+
+$initHandler = ini_get('session.save_handler');
+session_set_save_handler(new DummyHandler());
+$setHandler = ini_get('session.save_handler');
+var_dump($initHandler, $setHandler);
+?>
+--EXPECT--
+string(8) "whatever"
+string(4) "user"