diff --git a/src/engine/plugins/viaroute.cpp b/src/engine/plugins/viaroute.cpp
index c80c0411b..2a11a2e9d 100644
--- a/src/engine/plugins/viaroute.cpp
+++ b/src/engine/plugins/viaroute.cpp
@@ -121,9 +121,12 @@ ViaRoutePlugin::HandleRequest(const datafacade::ContiguousInternalMemoryDataFaca
         routes = algorithms.ShortestPathSearch(start_end_nodes, route_parameters.continue_straight);
     }
 
+    // The post condition for all path searches is we have at least one route in our result.
+    // This route might be invalid by means of INVALID_EDGE_WEIGHT as shortest path weight.
+    BOOST_ASSERT(!routes.routes.empty());
+
     // we can only know this after the fact, different SCC ids still
     // allow for connection in one direction.
-    BOOST_ASSERT(!routes.routes.empty());
 
     if (routes.routes[0].is_valid())
     {
diff --git a/src/engine/routing_algorithms/alternative_path_mld.cpp b/src/engine/routing_algorithms/alternative_path_mld.cpp
index 83f4a8e9b..0926bc99b 100644
--- a/src/engine/routing_algorithms/alternative_path_mld.cpp
+++ b/src/engine/routing_algorithms/alternative_path_mld.cpp
@@ -792,8 +792,15 @@ InternalManyRoutesResult alternativePathSearch(SearchEngineData<Algorithm> &sear
                                    shortest_path_via_it->node != SPECIAL_NODEID &&
                                    shortest_path_via_it->weight != INVALID_EDGE_WEIGHT;
 
+    // Care needs to be taken to meet the call sites post condition.
+    // We must return at least one route, even if it's an invalid one.
     if (!has_shortest_path)
-        return InternalManyRoutesResult{};
+    {
+        InternalRouteResult invalid;
+        invalid.shortest_path_weight = INVALID_EDGE_WEIGHT;
+        invalid.segment_end_coordinates = {phantom_node_pair};
+        return invalid;
+    }
 
     NodeID shortest_path_via = shortest_path_via_it->node;
     EdgeWeight shortest_path_weight = shortest_path_via_it->weight;