diff --git a/src/vs/workbench/api/node/extHostOutputService.ts b/src/vs/workbench/api/node/extHostOutputService.ts
index d6901a1c2be..b36f0bfb25e 100644
--- a/src/vs/workbench/api/node/extHostOutputService.ts
+++ b/src/vs/workbench/api/node/extHostOutputService.ts
@@ -35,18 +35,22 @@ export class ExtHostOutputChannel implements vscode.OutputChannel {
 	}
 
 	append(value: string): void {
+		this.validate();
 		this._proxy.$append(this._id, this._name, value);
 	}
 
 	appendLine(value: string): void {
+		this.validate();
 		this.append(value + '\n');
 	}
 
 	clear(): void {
+		this.validate();
 		this._proxy.$clear(this._id, this._name);
 	}
 
 	show(columnOrPreserveFocus?: vscode.ViewColumn | boolean, preserveFocus?: boolean): void {
+		this.validate();
 		if (typeof columnOrPreserveFocus === 'boolean') {
 			preserveFocus = columnOrPreserveFocus;
 		}
@@ -55,8 +59,15 @@ export class ExtHostOutputChannel implements vscode.OutputChannel {
 	}
 
 	hide(): void {
+		this.validate();
 		this._proxy.$close(this._id);
 	}
+
+	private validate(): void {
+		if (this._disposed) {
+			throw new Error('Channel has been closed');
+		}
+	}
 }
 
 export class ExtHostOutputService {