diff --git a/symmetri/tests/CMakeLists.txt b/symmetri/tests/CMakeLists.txt
index 1f29a45..615e0ab 100644
--- a/symmetri/tests/CMakeLists.txt
+++ b/symmetri/tests/CMakeLists.txt
@@ -13,11 +13,6 @@ FetchContent_Declare(
 # https://stackoverflow.com/questions/65527126/disable-install-for-fetchcontent
 FetchContent_GetProperties(concurrentqueue)
 
-if(NOT concurrentqueue_POPULATED)
-  FetchContent_Populate(concurrentqueue)
-  add_subdirectory(${concurrentqueue_SOURCE_DIR} ${concurrentqueue_BINARY_DIR} EXCLUDE_FROM_ALL)
-endif()
-
 include_directories(${EIGEN3_INCLUDE_DIRS} ../include ..)
 
 include(CTest)
diff --git a/symmetri/tests/test_external_input.cc b/symmetri/tests/test_external_input.cc
index 2e81b92..f66e146 100644
--- a/symmetri/tests/test_external_input.cc
+++ b/symmetri/tests/test_external_input.cc
@@ -1,37 +1,44 @@
 #include <catch2/catch_test_macros.hpp>
 #include <condition_variable>
+#include <mutex>
 
 #include "symmetri/symmetri.h"
 
 using namespace symmetri;
 
-std::atomic<bool> i_ran(false);
-void tExtInput() { i_ran.store(true); }
+std::atomic<bool> can_continue(false), done(false);
+void tAllowExitInput() {
+  can_continue.store(true);
+  while (!done.load()) {
+  }  // wait till trigger is done, otherwise we would deadlock
+}
 
 TEST_CASE("Test external input.") {
-  Net net = {
-      {"t0", {{}, {"Pa"}}}, {"t1", {{"Pa"}, {"Pb"}}}, {"t2", {{"Pc"}, {"Pb"}}}};
-  // we can omit t0, it will be auto-filled as {"t0", DirectMutation{}}
-  Store store = {{"t1", &tExtInput},
-                 {"t2", []() {
-                    std::this_thread::sleep_for(std::chrono::milliseconds(15));
-                  }}};
-  Marking m0 = {{"Pa", 0}, {"Pb", 0}, {"Pc", 1}};
-  Marking final_m = {{"Pb", 2}};
-  auto stp = std::make_shared<TaskSystem>(3);
-
-  PetriNet app(net, m0, final_m, store, {}, "test_net_ext_input", stp);
-
-  // enqueue a trigger;
-  stp->push([trigger = app.registerTransitionCallback("t0")]() {
-    // sleep a bit so it gets triggered _after_ the net started.
-    std::this_thread::sleep_for(std::chrono::milliseconds(10));
-    trigger();
-  });
-
-  // run the net
-  auto res = fire(app);
-
-  REQUIRE(res == state::Completed);
-  REQUIRE(i_ran);
+  {
+    Net net = {{"t0", {{}, {"Pb"}}},
+               {"t1", {{"Pa"}, {"Pb"}}},
+               {"t2", {{"Pb", "Pb"}, {"Pc"}}}};
+    // we can omit t0, it will be auto-filled as {"t0", DirectMutation{}}
+    Store store = {{"t1", &tAllowExitInput}, {"t2", DirectMutation{}}};
+    Marking m0 = {{"Pa", 2}, {"Pb", 0}, {"Pc", 0}};
+    Marking final_m = {{"Pc", 1}};
+    auto stp = std::make_shared<TaskSystem>(3);
+
+    PetriNet app(net, m0, final_m, store, {}, "test_net_ext_input", stp);
+
+    // enqueue a trigger;
+    stp->push([trigger = app.registerTransitionCallback("t0")]() {
+      // sleep a bit so it gets triggered _after_ the net started. Otherwise the
+      // net would deadlock
+      while (!can_continue.load()) {
+      }
+      trigger();
+      done.store(true);
+    });
+
+    // run the net
+    auto res = fire(app);
+    CHECK(can_continue);
+    CHECK(res == state::Completed);
+  }
 }