diff --git a/packages/plugin-ext/src/plugin/window-state.ts b/packages/plugin-ext/src/plugin/window-state.ts
index 160356282c8e9..4b4e58aac3bbd 100644
--- a/packages/plugin-ext/src/plugin/window-state.ts
+++ b/packages/plugin-ext/src/plugin/window-state.ts
@@ -19,7 +19,6 @@ import { WindowState } from '@theia/plugin';
 import { WindowStateExt, WindowMain, PLUGIN_RPC_CONTEXT } from '../common/plugin-api-rpc';
 import { Event, Emitter } from '@theia/core/lib/common/event';
 import { RPCProtocol } from '../common/rpc-protocol';
-import { Schemes } from '../common/uri-components';
 
 export class WindowStateExtImpl implements WindowStateExt {
 
@@ -50,6 +49,10 @@ export class WindowStateExtImpl implements WindowStateExt {
     }
 
     openUri(uri: URI): Promise<boolean> {
+        if (!uri.scheme.trim().length) {
+            throw new Error('Invalid scheme - cannot be empty');
+        }
+
         return this.proxy.$openUri(uri);
     }
 
@@ -57,9 +60,6 @@ export class WindowStateExtImpl implements WindowStateExt {
         if (!target.scheme.trim().length) {
             throw new Error('Invalid scheme - cannot be empty');
         }
-        if (Schemes.http !== target.scheme && Schemes.https !== target.scheme) {
-            throw new Error(`Invalid scheme '${target.scheme}'`);
-        }
 
         const uri = await this.proxy.$asExternalUri(target);
         return URI.revive(uri);