diff --git a/src/vs/workbench/api/node/extHost.protocol.ts b/src/vs/workbench/api/node/extHost.protocol.ts
index e4d9a3bc3f7..930889dba15 100644
--- a/src/vs/workbench/api/node/extHost.protocol.ts
+++ b/src/vs/workbench/api/node/extHost.protocol.ts
@@ -143,7 +143,6 @@ export abstract class MainThreadEditorsShape {
 
 export abstract class MainThreadTreeExplorersShape {
 	$registerTreeExplorerNodeProvider(providerId: string): void { throw ni(); }
-	$showMessage(severity: Severity, message: string): void { throw ni(); }
 }
 
 export abstract class MainThreadErrorsShape {
diff --git a/src/vs/workbench/api/node/extHostTreeExplorers.ts b/src/vs/workbench/api/node/extHostTreeExplorers.ts
index 2ea83e62426..4659b8f7acf 100644
--- a/src/vs/workbench/api/node/extHostTreeExplorers.ts
+++ b/src/vs/workbench/api/node/extHostTreeExplorers.ts
@@ -12,7 +12,6 @@ import { MainContext, ExtHostTreeExplorersShape, MainThreadTreeExplorersShape }
 import { InternalTreeExplorerNode } from 'vs/workbench/parts/explorers/common/treeExplorerViewModel';
 import { ExtHostCommands } from 'vs/workbench/api/node/extHostCommands';
 import { asWinJsPromise } from 'vs/base/common/async';
-import { Severity } from 'vs/platform/message/common/message';
 
 export class ExtHostTreeExplorers extends ExtHostTreeExplorersShape {
 	private _proxy: MainThreadTreeExplorersShape;
@@ -43,7 +42,10 @@ export class ExtHostTreeExplorers extends ExtHostTreeExplorersShape {
 	}
 
 	$provideRootNode(providerId: string): TPromise<InternalTreeExplorerNode> {
-		const provider = this.getProvider(providerId);
+		const provider = this._treeExplorerNodeProviders[providerId];
+		if (!provider) {
+			return TPromise.wrapError(`No TreeExplorerNodeProvider with id '${providerId}' registered.`);
+		}
 
 		return asWinJsPromise(() => provider.provideRootNode()).then(externalRootNode => {
 			const treeNodeMap = Object.create(null);
@@ -53,12 +55,15 @@ export class ExtHostTreeExplorers extends ExtHostTreeExplorersShape {
 			this._externalNodeMaps[providerId][internalRootNode.id] = externalRootNode;
 			return internalRootNode;
 		}, err => {
-			this.showErrorMessage(`TreeExplorerNodeProvider '${providerId}' failed to provide root node.`);
+			return TPromise.wrapError(`TreeExplorerNodeProvider '${providerId}' failed to provide root node.`);
 		});
 	}
 
 	$resolveChildren(providerId: string, mainThreadNode: InternalTreeExplorerNode): TPromise<InternalTreeExplorerNode[]> {
-		const provider = this.getProvider(providerId);
+		const provider = this._treeExplorerNodeProviders[providerId];
+		if (!provider) {
+			return TPromise.wrapError(`No TreeExplorerNodeProvider with id '${providerId}' registered.`);
+		}
 
 		const externalNodeMap = this._externalNodeMaps[providerId];
 		const externalNode = externalNodeMap[mainThreadNode.id];
@@ -70,7 +75,7 @@ export class ExtHostTreeExplorers extends ExtHostTreeExplorersShape {
 				return internalChild;
 			});
 		}, err => {
-			this.showErrorMessage(`TreeExplorerNodeProvider '${providerId}' failed to resolve children.`);
+			return TPromise.wrapError(`TreeExplorerNodeProvider '${providerId}' failed to resolve children.`);
 		});
 	}
 
@@ -80,23 +85,10 @@ export class ExtHostTreeExplorers extends ExtHostTreeExplorersShape {
 			return asWinJsPromise(() => this.commands.executeCommand(mainThreadNode.clickCommand, externalNode)).then(() => {
 				return null;
 			}, err => {
-				this.showErrorMessage(`Failed to execute command '${mainThreadNode.clickCommand}' provided by TreeExplorerNodeProvider '${providerId}'.`);
+				return TPromise.wrapError(`Failed to execute command '${mainThreadNode.clickCommand}' provided by TreeExplorerNodeProvider '${providerId}'.`);
 			});
 		}
 
 		return TPromise.as(null);
 	}
-
-	getProvider(providerId: string): TreeExplorerNodeProvider<any> {
-		const provider = this._treeExplorerNodeProviders[providerId];
-		if (!provider) {
-			this.showErrorMessage(`No TreeExplorerNodeProvider with id '${providerId}' registered.`);
-		}
-
-		return provider;
-	}
-
-	private showErrorMessage(message: string): void {
-		this._proxy.$showMessage(Severity.Error, message);
-	}
 }
diff --git a/src/vs/workbench/api/node/mainThreadTreeExplorers.ts b/src/vs/workbench/api/node/mainThreadTreeExplorers.ts
index 463051e0053..54ac3c368c2 100644
--- a/src/vs/workbench/api/node/mainThreadTreeExplorers.ts
+++ b/src/vs/workbench/api/node/mainThreadTreeExplorers.ts
@@ -15,7 +15,7 @@ export class MainThreadTreeExplorers extends MainThreadTreeExplorersShape {
 	private _proxy: ExtHostTreeExplorersShape;
 
 	constructor(
-		@IThreadService threadService: IThreadService,
+		@IThreadService private threadService: IThreadService,
 		@ITreeExplorerViewletService private treeExplorerService: ITreeExplorerViewletService,
 		@IMessageService private messageService: IMessageService
 	) {
@@ -25,20 +25,18 @@ export class MainThreadTreeExplorers extends MainThreadTreeExplorersShape {
 	}
 
 	$registerTreeExplorerNodeProvider(providerId: string): void {
+		const onError = err => { this.messageService.show(Severity.Error, err); };
+
 		this.treeExplorerService.registerTreeExplorerNodeProvider(providerId, {
 			provideRootNode: (): TPromise<InternalTreeExplorerNode> => {
-				return this._proxy.$provideRootNode(providerId);
+				return this._proxy.$provideRootNode(providerId).then(rootNode => rootNode, onError);
 			},
 			resolveChildren: (node: InternalTreeExplorerNode): TPromise<InternalTreeExplorerNode[]> => {
-				return this._proxy.$resolveChildren(providerId, node);
+				return this._proxy.$resolveChildren(providerId, node).then(children => children, onError);
 			},
 			executeCommand: (node: InternalTreeExplorerNode): TPromise<void> => {
 				return this._proxy.$executeCommand(providerId, node);
 			}
 		});
 	}
-
-	$showMessage(severity: Severity, message: string): void {
-		this.messageService.show(severity, message);
-	}
 }