diff --git a/src/tsconfig.strictNullChecks.json b/src/tsconfig.strictNullChecks.json
index a8c9d8f98495f162f587dfbd93680ea0b43a3bb0..385730e03cc947ee4cf130b76ed02776378ec054 100644
--- a/src/tsconfig.strictNullChecks.json
+++ b/src/tsconfig.strictNullChecks.json
@@ -430,6 +430,7 @@
 		"./vs/workbench/api/node/extHostMessageService.ts",
 		"./vs/workbench/api/node/extHostOutputService.ts",
 		"./vs/workbench/api/node/extHostSearch.fileIndex.ts",
+		"./vs/workbench/api/node/extHostSearch.ts",
 		"./vs/workbench/api/node/extHostStorage.ts",
 		"./vs/workbench/api/node/extHostTypes.ts",
 		"./vs/workbench/api/node/extHostUrls.ts",
diff --git a/src/vs/workbench/api/node/extHostSearch.ts b/src/vs/workbench/api/node/extHostSearch.ts
index d5a17a188097574fd956bf223869a270ac4374db..82c7aa8769a0bf07ece61fee0c0594594257919d 100644
--- a/src/vs/workbench/api/node/extHostSearch.ts
+++ b/src/vs/workbench/api/node/extHostSearch.ts
@@ -124,6 +124,10 @@ export class ExtHostSearch implements ExtHostSearchShape {
 				}, token);
 			} else {
 				const indexProvider = this._fileIndexProvider.get(handle);
+				if (!indexProvider) {
+					throw new Error('unknown provider: ' + handle);
+				}
+
 				return this._fileIndexSearchManager.fileSearch(query, indexProvider, batch => {
 					this._proxy.$handleFileMatch(handle, session, batch.map(p => p.resource));
 				}, token);
@@ -147,7 +151,11 @@ export class ExtHostSearch implements ExtHostSearchShape {
 			}
 		};
 
-		return this._internalFileSearchProvider.doFileSearch(rawQuery, onResult, token);
+		if (!this._internalFileSearchProvider) {
+			throw new Error('No internal file search handler');
+		}
+
+		return <Promise<ISearchCompleteStats>>this._internalFileSearchProvider.doFileSearch(rawQuery, onResult, token);
 	}
 
 	$clearCache(cacheKey: string): Promise<void> {
@@ -163,8 +171,8 @@ export class ExtHostSearch implements ExtHostSearchShape {
 
 	$provideTextSearchResults(handle: number, session: number, rawQuery: IRawTextQuery, token: CancellationToken): Promise<ISearchCompleteStats> {
 		const provider = this._textSearchProvider.get(handle);
-		if (!provider.provideTextSearchResults) {
-			return Promise.resolve(undefined);
+		if (!provider || !provider.provideTextSearchResults) {
+			throw new Error(`Unknown provider ${handle}`);
 		}
 
 		const query = reviveQuery(rawQuery);