diff --git a/src/vs/platform/extensionManagement/node/extensionManagementService.ts b/src/vs/platform/extensionManagement/node/extensionManagementService.ts
index 8e8a02f2069ff55351b43a04e1ba76ac32aa5015..6e98f58d13c16342c4cbeca19e622cf56550cdc0 100644
--- a/src/vs/platform/extensionManagement/node/extensionManagementService.ts
+++ b/src/vs/platform/extensionManagement/node/extensionManagementService.ts
@@ -301,7 +301,7 @@ export class ExtensionManagementService implements IExtensionManagementService {
 			if (local) {
 				this._onDidInstallExtension.fire({ identifier, gallery, local });
 			} else {
-				const errorCode = error && error instanceof InstallationError ? error.code : INSTALL_ERROR_UNKNOWN;
+				const errorCode = error && (<InstallationError>error).code ? (<InstallationError>error).code : INSTALL_ERROR_UNKNOWN;
 				this._onDidInstallExtension.fire({ identifier, gallery, error: errorCode });
 			}
 		});