diff --git a/src/engine/routing_algorithms/alternative_path_mld.cpp b/src/engine/routing_algorithms/alternative_path_mld.cpp
index 7bc14e5..5fffa63 100644
--- a/src/engine/routing_algorithms/alternative_path_mld.cpp
+++ b/src/engine/routing_algorithms/alternative_path_mld.cpp
@@ -683,6 +683,9 @@ makeCandidateVias(SearchEngineData<Algorithm> &search_engine_data,
     // we're over factor * weight. We have to set the weight for routingStep to INVALID_EDGE_WEIGHT
     // so that stepping will continue even after we reached the shortest path upper bound.

+    if (forward_heap.Empty())
+        return candidate_vias;
+
     EdgeWeight forward_heap_min = forward_heap.MinKey();
     EdgeWeight reverse_heap_min = reverse_heap.MinKey();

[assert][140490038109952] /src/osrm-backend/include/util/query_heap.hpp:280
in: Weight osrm::util::QueryHeap<NodeID, Key, Weight, Data, IndexStorage>::MinKey() const [with NodeID = unsigned int; Key = unsigned int; Weight = int; Data = osrm::engine::MultiLayerDijkstraHeapData; IndexStorage = osrm::util::TwoLevelStorage<unsigned int, int>]: !heap.empty()
terminate called without an active exception

Thread 4 "osrm-routed" received signal SIGABRT, Aborted.
[Switching to Thread 0x7fc662d0e700 (LWP 1548)]
__GI_raise (sig=sig@entry=6) at ../sysdeps/unix/sysv/linux/raise.c:50
50      ../sysdeps/unix/sysv/linux/raise.c: No such file or directory.
(gdb) bt
#0  __GI_raise (sig=sig@entry=6) at ../sysdeps/unix/sysv/linux/raise.c:50
#1  0x00007fc7df6e1859 in __GI_abort () at abort.c:79
#2  0x00007fc7dfab6951 in ?? () from /lib/x86_64-linux-gnu/libstdc++.so.6
#3  0x00007fc7dfac247c in ?? () from /lib/x86_64-linux-gnu/libstdc++.so.6
#4  0x00007fc7dfac24e7 in std::terminate() () from /lib/x86_64-linux-gnu/libstdc++.so.6
#5  0x0000563eb36b396e in (anonymous namespace)::assertion_failed_msg_helper (expr=expr@entry=0x563eb3849931 "!heap.empty()", msg=msg@entry=0x563eb3846f3c "",
    function=function@entry=0x563eb3874de8 "Weight osrm::util::QueryHeap<NodeID, Key, Weight, Data, IndexStorage>::MinKey() const [with NodeID = unsigned int; Key = unsigned int; Weight = int; Data = osrm::engine::MultiLayerDijkstraHeapData; In"..., file=file@entry=0x563eb3870c58 "/src/osrm-backend/include/util/query_heap.hpp", line=line@entry=280)
    at /src/osrm-backend/src/util/assert.cpp:19
#6  0x0000563eb36b398b in boost::assertion_failed (expr=expr@entry=0x563eb3849931 "!heap.empty()",
    function=function@entry=0x563eb3874de8 "Weight osrm::util::QueryHeap<NodeID, Key, Weight, Data, IndexStorage>::MinKey() const [with NodeID = unsigned int; Key = unsigned int; Weight = int; Data = osrm::engine::MultiLayerDijkstraHeapData; In"..., file=file@entry=0x563eb3870c58 "/src/osrm-backend/include/util/query_heap.hpp", line=line@entry=280)
    at /src/osrm-backend/src/util/assert.cpp:28
#7  0x0000563eb37e5c79 in osrm::util::QueryHeap<unsigned int, unsigned int, int, osrm::engine::MultiLayerDijkstraHeapData, osrm::util::TwoLevelStorage<unsigned int, int, osrm::util::UnorderedMapStorage, osrm::util::ArrayStorage> >::MinKey (this=this@entry=0x7fc6580038f0) at /src/osrm-backend/include/util/query_heap.hpp:278
#8  0x0000563eb37eddf2 in osrm::engine::routing_algorithms::(anonymous namespace)::makeCandidateVias (search_engine_data=..., facade=..., phantom_node_pair=..., parameters=...)
    at /src/osrm-backend/src/engine/routing_algorithms/alternative_path_mld.cpp:686
#9  0x0000563eb37efd98 in osrm::engine::routing_algorithms::alternativePathSearch (search_engine_data=..., facade=..., phantom_node_pair=...,
    number_of_alternatives=number_of_alternatives@entry=1) at /src/osrm-backend/src/engine/routing_algorithms/alternative_path_mld.cpp:796
#10 0x0000563eb3765d1f in osrm::engine::RoutingAlgorithms<osrm::engine::routing_algorithms::mld::Algorithm>::AlternativePathSearch (this=this@entry=0x7fc662d0caa0, phantom_node_pair=...,
    number_of_alternatives=number_of_alternatives@entry=1) at /src/osrm-backend/include/engine/routing_algorithms.hpp:154
#11 0x0000563eb37cf243 in osrm::engine::plugins::ViaRoutePlugin::HandleRequest (this=this@entry=0x563eb55824f4, algorithms=..., route_parameters=..., result=...)
    at /src/osrm-backend/src/engine/plugins/viaroute.cpp:124
#12 0x0000563eb3764e63 in osrm::engine::Engine<osrm::engine::routing_algorithms::mld::Algorithm>::Route (this=0x563eb55824e0, params=..., result=...)
    at /src/osrm-backend/include/engine/engine.hpp:88
#13 0x0000563eb374f2dd in osrm::OSRM::Route (this=this@entry=0x563eb55824d0, params=..., result=...) at /src/osrm-backend/src/osrm/osrm.cpp:62
#14 0x0000563eb36af348 in osrm::server::service::RouteService::RunQuery (this=0x563eb55835a0, prefix_length=18, query=..., result=...)
    at /src/osrm-backend/src/server/service/route_service.cpp:74
#15 0x0000563eb36b350e in osrm::server::ServiceHandler::RunQuery (this=this@entry=0x563eb5582490, parsed_url=..., result=...) at /src/osrm-backend/src/server/service_handler.cpp:52
#16 0x0000563eb36a2aa5 in osrm::server::RequestHandler::HandleRequest (this=<optimized out>, current_request=..., current_reply=...) at /src/osrm-backend/src/server/request_handler.cpp:69
#17 0x0000563eb3698ae7 in osrm::server::Connection::handle_read (this=0x7fc654000cd0, error=..., bytes_transferred=<optimized out>) at /src/osrm-backend/src/server/connection.cpp:79
#18 0x0000563eb36942e5 in boost::_mfi::mf2<void, osrm::server::Connection, boost::system::error_code const&, unsigned long>::call<std::shared_ptr<osrm::server::Connection>, boost::system::error_code const, unsigned long> (this=this@entry=0x7fc662d0d730, u=..., b1=..., b2=@0x7fc662d0d448: 158, b2@entry=@0x7fc662d0d448: <optimized out>)
    at /usr/include/boost/bind/mem_fn_template.hpp:269
#19 0x0000563eb3694311 in boost::_mfi::mf2<void, osrm::server::Connection, boost::system::error_code const&, unsigned long>::operator()<std::shared_ptr<osrm::server::Connection> > (
    this=this@entry=0x7fc662d0d730, u=..., a1=..., a2=<optimized out>) at /usr/include/boost/bind/mem_fn_template.hpp:283
#20 0x0000563eb369437f in boost::_bi::list3<boost::_bi::value<std::shared_ptr<osrm::server::Connection> >, boost::arg<1> (*)(), boost::arg<2> (*)()>::operator()<boost::_mfi::mf2<void, osrm::server::Connection, boost::system::error_code const&, unsigned long>, boost::_bi::rrlist2<boost::system::error_code const&, unsigned long const&> > (this=this@entry=0x7fc662d0d740,
    f=..., a=...) at /usr/include/boost/bind/bind.hpp:396
#21 0x0000563eb36943d3 in boost::_bi::bind_t<void, boost::_mfi::mf2<void, osrm::server::Connection, boost::system::error_code const&, unsigned long>, boost::_bi::list3<boost::_bi::value<std::shared_ptr<osrm::server::Connection> >, boost::arg<1> (*)(), boost::arg<2> (*)()> >::operator()<boost::system::error_code const&, unsigned long const&> (this=0x7fc662d0d730, a1=...,
    a2=<optimized out>) at /usr/include/boost/bind/bind.hpp:1315
#22 0x0000563eb3694403 in boost::asio::detail::binder2<boost::_bi::bind_t<void, boost::_mfi::mf2<void, osrm::server::Connection, boost::system::error_code const&, unsigned long>, boost::_bi::list3<boost::_bi::value<std::shared_ptr<osrm::server::Connection> >, boost::arg<1> (*)(), boost::arg<2> (*)()> >, boost::system::error_code, unsigned long>::operator() (
    this=<optimized out>) at /usr/include/boost/asio/detail/bind_handler.hpp:162
#23 0x0000563eb3694460 in boost::asio::asio_handler_invoke<boost::asio::detail::binder2<boost::_bi::bind_t<void, boost::_mfi::mf2<void, osrm::server::Connection, boost::system::error_code const&, unsigned long>, boost::_bi::list3<boost::_bi::value<std::shared_ptr<osrm::server::Connection> >, boost::arg<1> (*)(), boost::arg<2> (*)()> >, boost::system::error_code, unsigned long> > (function=...) at /usr/include/boost/asio/handler_invoke_hook.hpp:67
#24 0x0000563eb369448a in boost_asio_handler_invoke_helpers::invoke<boost::asio::detail::binder2<boost::_bi::bind_t<void, boost::_mfi::mf2<void, osrm::server::Connection, boost::system::err--Type <RET> for more, q to quit, c to continue without paging--q