diff --git a/packages/markers/src/common/marker.ts b/packages/markers/src/common/marker.ts
index 4a5bf25f717bc..54b532450a4e4 100644
--- a/packages/markers/src/common/marker.ts
+++ b/packages/markers/src/common/marker.ts
@@ -40,14 +40,16 @@ export interface Marker<T> {
     data: T;
 }
 export namespace Marker {
-    export function is(value: unknown): value is Marker<object>;
-    export function is<T>(value: unknown, subTypeCheck: (value: unknown) => value is T): value is Marker<T>;
-    export function is(value: unknown, subTypeCheck?: (value: unknown) => boolean): boolean {
-        subTypeCheck ??= isObject;
+
+    export function is<T>(value: unknown, subTypeCheck: (value: unknown) => value is T): value is Marker<T> {
         return isObject<Marker<object>>(value)
             && !Array.isArray(value)
             && subTypeCheck(value.data)
             && isString(value.uri)
             && isString(value.owner);
     }
+
+    export function isMarkerObject(value: unknown): value is Marker<object> {
+        return is(value, isObject);
+    }
 }
diff --git a/packages/markers/src/common/problem-marker.ts b/packages/markers/src/common/problem-marker.ts
index a9e56a4efbecb..76fec1a8875c1 100644
--- a/packages/markers/src/common/problem-marker.ts
+++ b/packages/markers/src/common/problem-marker.ts
@@ -25,6 +25,6 @@ export interface ProblemMarker extends Marker<Diagnostic> {
 
 export namespace ProblemMarker {
     export function is(node: unknown): node is ProblemMarker {
-        return Marker.is(node) && node.kind === PROBLEM_KIND;
+        return Marker.isMarkerObject(node) && node.kind === PROBLEM_KIND;
     }
 }