diff --git a/src/vs/base/common/glob.ts b/src/vs/base/common/glob.ts
index 4837cc12f55f0a8bd96344e7cf281e8f941165a6..7e11d8c18c0789ddb2df7bb38742707e3a18935d 100644
--- a/src/vs/base/common/glob.ts
+++ b/src/vs/base/common/glob.ts
@@ -482,7 +482,7 @@ export function parse(arg1: string | IExpression | IRelativePattern, options: IG
 	return parsedExpression(<IExpression>arg1, options);
 }
 
-function isRelativePattern(obj: any): obj is IRelativePattern {
+export function isRelativePattern(obj: any): obj is IRelativePattern {
 	const rp = obj as IRelativePattern;
 
 	return typeof rp.base === 'string' && typeof rp.pattern === 'string';
diff --git a/src/vs/workbench/api/electron-browser/mainThreadWorkspace.ts b/src/vs/workbench/api/electron-browser/mainThreadWorkspace.ts
index 5105287b174e18864ee9c86a429e7eb59b522fda..837eb4f98a3bfe57324f7fbb5203f5bbf18267c9 100644
--- a/src/vs/workbench/api/electron-browser/mainThreadWorkspace.ts
+++ b/src/vs/workbench/api/electron-browser/mainThreadWorkspace.ts
@@ -14,7 +14,7 @@ import { MainThreadWorkspaceShape, ExtHostWorkspaceShape, ExtHostContext, MainCo
 import { IDisposable, dispose } from 'vs/base/common/lifecycle';
 import { extHostNamedCustomer } from 'vs/workbench/api/electron-browser/extHostCustomers';
 import { IConfigurationService } from 'vs/platform/configuration/common/configuration';
-import { IRelativePattern } from 'vs/base/common/glob';
+import { IRelativePattern, isRelativePattern } from 'vs/base/common/glob';
 
 @extHostNamedCustomer(MainContext.MainThreadWorkspace)
 export class MainThreadWorkspace implements MainThreadWorkspaceShape {
@@ -61,10 +61,14 @@ export class MainThreadWorkspace implements MainThreadWorkspaceShape {
 		let folderQueries: IFolderQuery[];
 		if (typeof include === 'string' || !include) {
 			folderQueries = workspace.folders.map(folder => ({ folder: folder.uri })); // absolute pattern: search across all folders
-		} else {
+		} else if (isRelativePattern(include)) {
 			folderQueries = [{ folder: URI.file(include.base) }]; // relative pattern: search only in base folder
 		}
 
+		if (!folderQueries) {
+			return undefined; // invalid query parameters
+		}
+
 		const useRipgrep = folderQueries.every(folderQuery => {
 			const folderConfig = this._configurationService.getValue<ISearchConfiguration>({ resource: folderQuery.folder });
 			return folderConfig.search.useRipgrep;