diff --git a/src/harness/fourslash.ts b/src/harness/fourslash.ts
index 79dd86ccb092d..4b9816f9fcb05 100644
--- a/src/harness/fourslash.ts
+++ b/src/harness/fourslash.ts
@@ -2819,7 +2819,7 @@ Actual: ${stringify(fullActual)}`);
             }
         }
 
-        private getDocumentHighlightsAtCurrentPosition(fileNamesToSearch: string[]) {
+        private getDocumentHighlightsAtCurrentPosition(fileNamesToSearch: ReadonlyArray<string>) {
             const filesToSearch = fileNamesToSearch.map(name => ts.combinePaths(this.basePath, name));
             return this.languageService.getDocumentHighlights(this.activeFile.fileName, this.currentCaretPosition, filesToSearch);
         }
@@ -2843,9 +2843,8 @@ Actual: ${stringify(fullActual)}`);
             this.rangesByText().forEach(ranges => this.verifyRangesAreDocumentHighlights(ranges));
         }
 
-        public verifyDocumentHighlightsOf(startRange: Range, ranges: Range[]) {
-            ts.Debug.assert(ts.contains(ranges, startRange));
-            const fileNames = unique(ranges, range => range.fileName);
+        public verifyDocumentHighlightsOf(startRange: Range, ranges: Range[], options: FourSlashInterface.VerifyDocumentHighlightsOptions | undefined) {
+            const fileNames = options && options.filesToSearch || unique(ranges, range => range.fileName);
             this.goToRangeStart(startRange);
             this.verifyDocumentHighlights(ranges, fileNames);
         }
@@ -2868,7 +2867,7 @@ Actual: ${stringify(fullActual)}`);
             }
         }
 
-        private verifyDocumentHighlights(expectedRanges: Range[], fileNames: string[] = [this.activeFile.fileName]) {
+        private verifyDocumentHighlights(expectedRanges: Range[], fileNames: ReadonlyArray<string> = [this.activeFile.fileName]) {
             const documentHighlights = this.getDocumentHighlightsAtCurrentPosition(fileNames) || [];
 
             for (const dh of documentHighlights) {
@@ -2880,10 +2879,7 @@ Actual: ${stringify(fullActual)}`);
             for (const fileName of fileNames) {
                 const expectedRangesInFile = expectedRanges.filter(r => r.fileName === fileName);
                 const highlights = ts.find(documentHighlights, dh => dh.fileName === fileName);
-                if (!highlights) {
-                    this.raiseError(`verifyDocumentHighlights failed - found no highlights in ${fileName}`);
-                }
-                const spansInFile = highlights.highlightSpans.sort((s1, s2) => s1.textSpan.start - s2.textSpan.start);
+                const spansInFile = highlights ? highlights.highlightSpans.sort((s1, s2) => s1.textSpan.start - s2.textSpan.start) : [];
 
                 if (expectedRangesInFile.length !== spansInFile.length) {
                     this.raiseError(`verifyDocumentHighlights failed - In ${fileName}, expected ${expectedRangesInFile.length} highlights, got ${spansInFile.length}`);
@@ -4272,8 +4268,8 @@ namespace FourSlashInterface {
             this.state.verifyRangesWithSameTextAreDocumentHighlights();
         }
 
-        public documentHighlightsOf(startRange: FourSlash.Range, ranges: FourSlash.Range[]) {
-            this.state.verifyDocumentHighlightsOf(startRange, ranges);
+        public documentHighlightsOf(startRange: FourSlash.Range, ranges: FourSlash.Range[], options?: VerifyDocumentHighlightsOptions) {
+            this.state.verifyDocumentHighlightsOf(startRange, ranges, options);
         }
 
         public noDocumentHighlights(startRange: FourSlash.Range) {
@@ -4622,6 +4618,10 @@ namespace FourSlashInterface {
         insertText?: string;
     }
 
+    export interface VerifyDocumentHighlightsOptions {
+        filesToSearch?: ReadonlyArray<string>;
+    }
+
     export interface NewContentOptions {
         // Exactly one of these should be defined.
         newFileContent?: string;
diff --git a/src/services/services.ts b/src/services/services.ts
index ddb869624a858..422248465c9d9 100644
--- a/src/services/services.ts
+++ b/src/services/services.ts
@@ -1582,7 +1582,7 @@ namespace ts {
 
         function getDocumentHighlights(fileName: string, position: number, filesToSearch: string[]): DocumentHighlights[] {
             synchronizeHostData();
-            const sourceFilesToSearch = map(filesToSearch, f => program.getSourceFile(f));
+            const sourceFilesToSearch = map(filesToSearch, f => Debug.assertDefined(program.getSourceFile(f)));
             const sourceFile = getValidSourceFile(fileName);
             return DocumentHighlights.getDocumentHighlights(program, cancellationToken, sourceFile, position, sourceFilesToSearch);
         }
diff --git a/tests/cases/fourslash/fourslash.ts b/tests/cases/fourslash/fourslash.ts
index 774c2191fd069..1d7cb0810f4de 100644
--- a/tests/cases/fourslash/fourslash.ts
+++ b/tests/cases/fourslash/fourslash.ts
@@ -310,7 +310,9 @@ declare namespace FourSlashInterface {
         occurrencesAtPositionCount(expectedCount: number): void;
         rangesAreDocumentHighlights(ranges?: Range[]): void;
         rangesWithSameTextAreDocumentHighlights(): void;
-        documentHighlightsOf(startRange: Range, ranges: Range[]): void;
+        documentHighlightsOf(startRange: Range, ranges: Range[], options?: {
+            filesToSearch?: ReadonlyArray<string>;
+        }): void;
         completionEntryDetailIs(entryName: string, text: string, documentation?: string, kind?: string, tags?: ts.JSDocTagInfo[]): void;
         /**
          * This method *requires* a contiguous, complete, and ordered stream of classifications for a file.