diff --git a/src/vs/workbench/api/electron-browser/mainThreadLanguageFeatures.ts b/src/vs/workbench/api/electron-browser/mainThreadLanguageFeatures.ts
index cf46b6138e2..8ae09ea6f35 100644
--- a/src/vs/workbench/api/electron-browser/mainThreadLanguageFeatures.ts
+++ b/src/vs/workbench/api/electron-browser/mainThreadLanguageFeatures.ts
@@ -232,7 +232,8 @@ export class MainThreadLanguageFeatures implements MainThreadLanguageFeaturesSha
 
 	// --- suggest
 
-	$registerSuggestSupport(handle: number, selector: vscode.DocumentSelector, triggerCharacters: string[]): TPromise<any> {
+	$registerSuggestSupport(handle: number, selector: vscode.DocumentSelector, triggerCharacters: string[], supportsResolveDetails: boolean): TPromise<any> {
+
 		this._registrations[handle] = modes.SuggestRegistry.register(selector, <modes.ISuggestSupport>{
 			triggerCharacters,
 			provideCompletionItems: (model: IReadOnlyModel, position: EditorPosition, token: CancellationToken): Thenable<modes.ISuggestResult> => {
@@ -247,9 +248,9 @@ export class MainThreadLanguageFeatures implements MainThreadLanguageFeaturesSha
 					};
 				});
 			},
-			resolveCompletionItem: (model: IReadOnlyModel, position: EditorPosition, suggestion: modes.ISuggestion, token: CancellationToken): Thenable<modes.ISuggestion> => {
-				return wireCancellationToken(token, this._proxy.$resolveCompletionItem(handle, model.uri, position, suggestion));
-			}
+			resolveCompletionItem: supportsResolveDetails
+				? (model, position, suggestion, token) => wireCancellationToken(token, this._proxy.$resolveCompletionItem(handle, model.uri, position, suggestion))
+				: undefined
 		});
 		return undefined;
 	}
diff --git a/src/vs/workbench/api/node/extHost.protocol.ts b/src/vs/workbench/api/node/extHost.protocol.ts
index 8e83b760583..5f6c6451184 100644
--- a/src/vs/workbench/api/node/extHost.protocol.ts
+++ b/src/vs/workbench/api/node/extHost.protocol.ts
@@ -229,7 +229,7 @@ export interface MainThreadLanguageFeaturesShape extends IDisposable {
 	$registerOnTypeFormattingSupport(handle: number, selector: vscode.DocumentSelector, autoFormatTriggerCharacters: string[]): TPromise<any>;
 	$registerNavigateTypeSupport(handle: number): TPromise<any>;
 	$registerRenameSupport(handle: number, selector: vscode.DocumentSelector): TPromise<any>;
-	$registerSuggestSupport(handle: number, selector: vscode.DocumentSelector, triggerCharacters: string[]): TPromise<any>;
+	$registerSuggestSupport(handle: number, selector: vscode.DocumentSelector, triggerCharacters: string[], supportsResolveDetails: boolean): TPromise<any>;
 	$registerSignatureHelpProvider(handle: number, selector: vscode.DocumentSelector, triggerCharacter: string[]): TPromise<any>;
 	$registerDocumentLinkProvider(handle: number, selector: vscode.DocumentSelector): TPromise<any>;
 	$registerColorFormats(formats: IRawColorFormatMap): TPromise<any>;
diff --git a/src/vs/workbench/api/node/extHostLanguageFeatures.ts b/src/vs/workbench/api/node/extHostLanguageFeatures.ts
index 49800798ce8..b877218b528 100644
--- a/src/vs/workbench/api/node/extHostLanguageFeatures.ts
+++ b/src/vs/workbench/api/node/extHostLanguageFeatures.ts
@@ -469,6 +469,10 @@ class RenameAdapter {
 
 class SuggestAdapter {
 
+	static supportsResolving(provider: vscode.CompletionItemProvider): boolean {
+		return typeof provider.resolveCompletionItem === 'function';
+	}
+
 	private _documents: ExtHostDocuments;
 	private _commands: CommandsConverter;
 	private _provider: vscode.CompletionItemProvider;
@@ -1002,7 +1006,7 @@ export class ExtHostLanguageFeatures implements ExtHostLanguageFeaturesShape {
 	registerCompletionItemProvider(selector: vscode.DocumentSelector, provider: vscode.CompletionItemProvider, triggerCharacters: string[]): vscode.Disposable {
 		const handle = this._nextHandle();
 		this._adapter.set(handle, new SuggestAdapter(this._documents, this._commands.converter, provider));
-		this._proxy.$registerSuggestSupport(handle, selector, triggerCharacters);
+		this._proxy.$registerSuggestSupport(handle, selector, triggerCharacters, SuggestAdapter.supportsResolving(provider));
 		return this._createDisposable(handle);
 	}