diff --git a/build/package.json b/build/package.json
index b30fd3b92c27f12c4bd7bb45889352a53cf56562..9302d56f2f6fff0b2739d59cec366793d9c63d98 100644
--- a/build/package.json
+++ b/build/package.json
@@ -43,7 +43,7 @@
     "minimist": "^1.2.2",
     "request": "^2.85.0",
     "terser": "4.3.8",
-    "typescript": "^3.9.0-dev.20200316",
+    "typescript": "^3.9.0-dev.20200327",
     "vsce": "1.48.0",
     "vscode-telemetry-extractor": "^1.5.4",
     "xml2js": "^0.4.17"
diff --git a/build/yarn.lock b/build/yarn.lock
index e3fde9ae0ca8d58a6ac78a6abca1ada12d391c0f..298e9596f12838664ee51fe96c05cdc7e7bb1c58 100644
--- a/build/yarn.lock
+++ b/build/yarn.lock
@@ -2458,10 +2458,10 @@ typescript@^3.0.1:
   resolved "https://registry.yarnpkg.com/typescript/-/typescript-3.5.3.tgz#c830f657f93f1ea846819e929092f5fe5983e977"
   integrity sha512-ACzBtm/PhXBDId6a6sDJfroT2pOWt/oOnk4/dElG5G33ZL776N3Y6/6bKZJBFpd+b05F3Ct9qDjMeJmRWtE2/g==
 
-typescript@^3.9.0-dev.20200316:
-  version "3.9.0-dev.20200316"
-  resolved "https://registry.yarnpkg.com/typescript/-/typescript-3.9.0-dev.20200316.tgz#7cbb2fa2eedf58eea27b3250ab38674790ccf999"
-  integrity sha512-MM67isAuvHM4hwfHR4K9NikB7MFD9RjISB5cXhtKmjkpMFO0QNzFmFq061VmsJqoRVpG9N2KE+cm6BJ9dIjrtQ==
+typescript@^3.9.0-dev.20200327:
+  version "3.9.0-dev.20200327"
+  resolved "https://registry.yarnpkg.com/typescript/-/typescript-3.9.0-dev.20200327.tgz#52179aae816587f772a0526e91143760f2bee42f"
+  integrity sha512-/TWD/zPvhAcN2Toqx2NBQ+oDVGVj4iqupjWcUAwL45TfcODeHpzszneABR1b/EjHbtUObtLH40vy5Z6rdVvKzg==
 
 typical@^4.0.0:
   version "4.0.0"
diff --git a/package.json b/package.json
index 3993f7c354ca674d5fc1b43ed0de91bfe19e9cbb..9c3cb9199d0cca644f3e7369cc5efa103e4e2ee8 100644
--- a/package.json
+++ b/package.json
@@ -150,7 +150,7 @@
     "source-map": "^0.4.4",
     "style-loader": "^1.0.0",
     "ts-loader": "^4.4.2",
-    "typescript": "^3.9.0-dev.20200316",
+    "typescript": "^3.9.0-dev.20200327",
     "typescript-formatter": "7.1.0",
     "underscore": "^1.8.2",
     "vinyl": "^2.0.0",
diff --git a/src/vs/base/browser/ui/tree/asyncDataTree.ts b/src/vs/base/browser/ui/tree/asyncDataTree.ts
index f42dc7d31ebe245c2365d7640230e75d58f745df..35a093fd21481c388f8e1205c00a1da03c8b522d 100644
--- a/src/vs/base/browser/ui/tree/asyncDataTree.ts
+++ b/src/vs/base/browser/ui/tree/asyncDataTree.ts
@@ -269,7 +269,7 @@ function asObjectTreeOptions<TInput, T, TFilterData>(options?: IAsyncDataTreeOpt
 				return options.ariaProvider!.getRole!(el.element as T);
 			} : () => 'treeitem',
 			isChecked: options.ariaProvider!.isChecked ? (e) => {
-				return options.ariaProvider?.isChecked!(e.element as T);
+				return !!(options.ariaProvider?.isChecked!(e.element as T));
 			} : undefined
 		},
 		ariaRole: ListAriaRootRole.TREE,
diff --git a/src/vs/workbench/contrib/search/common/searchModel.ts b/src/vs/workbench/contrib/search/common/searchModel.ts
index f063edc3eb9e30d8829bbc5176aab0e95a5ee90b..ca24d175027d403a71aff3a898927ff47858a171 100644
--- a/src/vs/workbench/contrib/search/common/searchModel.ts
+++ b/src/vs/workbench/contrib/search/common/searchModel.ts
@@ -606,7 +606,7 @@ export class FolderMatch extends Disposable {
 			fileMatches = [fileMatches];
 		}
 
-		for (let match of fileMatches) {
+		for (let match of fileMatches as FileMatch[]) {
 			this._fileMatches.delete(match.resource);
 			if (dispose) {
 				match.dispose();
diff --git a/yarn.lock b/yarn.lock
index 5580df3276a94b7599d0925eaab750ad3d889995..3010fbb87bc6417680e5ad54fa26823189dc7437 100644
--- a/yarn.lock
+++ b/yarn.lock
@@ -9224,10 +9224,10 @@ typescript@^2.6.2:
   resolved "https://registry.yarnpkg.com/typescript/-/typescript-2.6.2.tgz#3c5b6fd7f6de0914269027f03c0946758f7673a4"
   integrity sha1-PFtv1/beCRQmkCfwPAlGdY92c6Q=
 
-typescript@^3.9.0-dev.20200316:
-  version "3.9.0-dev.20200316"
-  resolved "https://registry.yarnpkg.com/typescript/-/typescript-3.9.0-dev.20200316.tgz#7cbb2fa2eedf58eea27b3250ab38674790ccf999"
-  integrity sha512-MM67isAuvHM4hwfHR4K9NikB7MFD9RjISB5cXhtKmjkpMFO0QNzFmFq061VmsJqoRVpG9N2KE+cm6BJ9dIjrtQ==
+typescript@^3.9.0-dev.20200327:
+  version "3.9.0-dev.20200327"
+  resolved "https://registry.yarnpkg.com/typescript/-/typescript-3.9.0-dev.20200327.tgz#52179aae816587f772a0526e91143760f2bee42f"
+  integrity sha512-/TWD/zPvhAcN2Toqx2NBQ+oDVGVj4iqupjWcUAwL45TfcODeHpzszneABR1b/EjHbtUObtLH40vy5Z6rdVvKzg==
 
 uc.micro@^1.0.1, uc.micro@^1.0.3:
   version "1.0.3"