diff --git a/source/extensions/filters/network/thrift_proxy/router/router_impl.h b/source/extensions/filters/network/thrift_proxy/router/router_impl.h
index 78afddfaf3970..60bac99805940 100644
--- a/source/extensions/filters/network/thrift_proxy/router/router_impl.h
+++ b/source/extensions/filters/network/thrift_proxy/router/router_impl.h
@@ -95,7 +95,11 @@ class RouteEntryImplBase : public RouteEntry,
     }
     const RateLimitPolicy& rateLimitPolicy() const override { return parent_.rateLimitPolicy(); }
     bool stripServiceName() const override { return parent_.stripServiceName(); }
-    const Http::LowerCaseString& clusterHeader() const override { return parent_.clusterHeader(); }
+    const Http::LowerCaseString& clusterHeader() const override {
+      // Weighted cluster entries don't have a cluster header based on proto.
+      ASSERT(parent_.clusterHeader().get().empty());
+      return parent_.clusterHeader();
+    }
     const std::vector<std::shared_ptr<RequestMirrorPolicy>>&
     requestMirrorPolicies() const override {
       return parent_.requestMirrorPolicies();