diff --git a/src/vs/editor/contrib/parameterHints/parameterHintsWidget.ts b/src/vs/editor/contrib/parameterHints/parameterHintsWidget.ts
index 80983c2bac790113b70443e11ef20bf15658ebf3..970799fb896c07c4289a01395a1089c5470f9737 100644
--- a/src/vs/editor/contrib/parameterHints/parameterHintsWidget.ts
+++ b/src/vs/editor/contrib/parameterHints/parameterHintsWidget.ts
@@ -209,7 +209,7 @@ export class ParameterHintsWidget extends Disposable implements IContentWidget {
 
 		this.renderDisposeables.clear();
 
-		const activeParameter = signature.parameters[hints.activeParameter];
+		const activeParameter: modes.ParameterInformation | undefined = signature.parameters[hints.activeParameter];
 
 		if (activeParameter && activeParameter.documentation) {
 			const documentation = $('span.documentation');