diff --git a/src/api/sorting/plugin_sort.cpp b/src/api/sorting/plugin_sort.cpp
index be5c98df..f19b85a6 100644
--- a/src/api/sorting/plugin_sort.cpp
+++ b/src/api/sorting/plugin_sort.cpp
@@ -100,6 +100,78 @@ std::unordered_map<std::string, Group> GetGroupsMap(
   return groupsMap;
 }
 
+void ValidateSpecificAndHardcodedEdges(
+    const std::vector<PluginSortingData>::const_iterator& begin,
+    const std::vector<PluginSortingData>::const_iterator& firstNonMaster,
+    const std::vector<PluginSortingData>::const_iterator& end,
+    const std::vector<std::string>& hardcodedPlugins) {
+  const auto isNonMaster = [&](const std::string& name) {
+    return std::any_of(
+        firstNonMaster, end, [&](const PluginSortingData& plugin) {
+          return CompareFilenames(plugin.GetName(), name) == 0;
+        });
+  };
+
+  for (auto it = begin; it != firstNonMaster; ++it) {
+    for (const auto& master : it->GetMasters()) {
+      if (isNonMaster(master)) {
+        throw CyclicInteractionError(
+            std::vector<Vertex>{Vertex(master, EdgeType::master),
+                                Vertex(it->GetName(), EdgeType::masterFlag)});
+      }
+    }
+
+    for (const auto& file : it->GetMasterlistRequirements()) {
+      const auto name = std::string(file.GetName());
+      if (isNonMaster(name)) {
+        throw CyclicInteractionError(
+            std::vector<Vertex>{Vertex(name, EdgeType::masterlistRequirement),
+                                Vertex(it->GetName(), EdgeType::masterFlag)});
+      }
+    }
+
+    for (const auto& file : it->GetUserRequirements()) {
+      const auto name = std::string(file.GetName());
+      if (isNonMaster(name)) {
+        throw CyclicInteractionError(
+            std::vector<Vertex>{Vertex(name, EdgeType::userRequirement),
+                                Vertex(it->GetName(), EdgeType::masterFlag)});
+      }
+    }
+
+    for (const auto& file : it->GetMasterlistLoadAfterFiles()) {
+      const auto name = std::string(file.GetName());
+      if (isNonMaster(name)) {
+        throw CyclicInteractionError(
+            std::vector<Vertex>{Vertex(name, EdgeType::masterlistLoadAfter),
+                                Vertex(it->GetName(), EdgeType::masterFlag)});
+      }
+    }
+
+    for (const auto& file : it->GetUserLoadAfterFiles()) {
+      const auto name = std::string(file.GetName());
+      if (isNonMaster(name)) {
+        throw CyclicInteractionError(
+            std::vector<Vertex>{Vertex(name, EdgeType::userLoadAfter),
+                                Vertex(it->GetName(), EdgeType::masterFlag)});
+      }
+    }
+  }
+
+  if (begin != firstNonMaster) {
+    // There's at least one master, check that there are no hardcoded
+    // non-masters.
+    for (const auto& plugin : hardcodedPlugins) {
+      if (isNonMaster(plugin)) {
+        // Just report the cycle to the first master.
+        throw CyclicInteractionError(std::vector<Vertex>{
+            Vertex(plugin, EdgeType::hardcoded),
+            Vertex(begin->GetName(), EdgeType::masterFlag)});
+      }
+    }
+  }
+}
+
 std::vector<std::string> SortPlugins(
     const std::vector<PluginSortingData>::const_iterator& begin,
     const std::vector<PluginSortingData>::const_iterator& end,
@@ -195,6 +267,11 @@ std::vector<std::string> SortPlugins(
       pluginsSortingData.end(),
       [](const PluginSortingData& plugin) { return plugin.IsMaster(); });
 
+  ValidateSpecificAndHardcodedEdges(pluginsSortingData.begin(),
+                                    firstNonMasterIt,
+                                    pluginsSortingData.end(),
+                                    hardcodedPlugins);
+
   auto newLoadOrder = SortPlugins(pluginsSortingData.begin(),
                                   firstNonMasterIt,
                                   hardcodedPlugins,
diff --git a/src/tests/api/internals/sorting/plugin_graph_test.h b/src/tests/api/internals/sorting/plugin_graph_test.h
index 4d3cd44f..e275a743 100644
--- a/src/tests/api/internals/sorting/plugin_graph_test.h
+++ b/src/tests/api/internals/sorting/plugin_graph_test.h
@@ -56,7 +56,7 @@ public:
     return std::optional<uint32_t>();
   }
 
-  bool IsMaster() const override { return false; }
+  bool IsMaster() const override { return isMaster_; }
 
   bool IsLightPlugin() const override { return false; }
 
@@ -93,6 +93,8 @@ public:
 
   void AddMaster(const std::string& master) { masters_.push_back(master); }
 
+  void SetIsMaster(bool isMaster) { isMaster_ = isMaster; }
+
   void AddOverlappingRecords(const PluginInterface& plugin) {
     recordsOverlapWith.insert(&plugin);
   }
@@ -114,6 +116,7 @@ private:
   std::set<const PluginSortingInterface*> assetsOverlapWith;
   size_t overrideRecordCount_{0};
   size_t assetCount_{0};
+  bool isMaster_{false};
 };
 }
 
diff --git a/src/tests/api/internals/sorting/plugin_sort_test.h b/src/tests/api/internals/sorting/plugin_sort_test.h
index 65831805..8b5b7687 100644
--- a/src/tests/api/internals/sorting/plugin_sort_test.h
+++ b/src/tests/api/internals/sorting/plugin_sort_test.h
@@ -92,7 +92,7 @@ protected:
 
   PluginSortingData CreatePluginSortingData(
       const std::string& name,
-      const std::vector<std::string>& loadOrder) {
+      const std::vector<std::string>& loadOrder = {}) {
     const auto plugin = GetPlugin(name);
 
     return PluginSortingData(plugin,
@@ -407,6 +407,177 @@ TEST_P(PluginSortTest, sortingShouldThrowIfACyclicInteractionIsEncountered) {
   EXPECT_THROW(SortPlugins(game_, game_.GetLoadOrder()),
                CyclicInteractionError);
 }
+
+TEST_P(PluginSortTest,
+       sortingShouldThrowIfMasterEdgeWouldContradictMasterFlags) {
+  // Can't test with the test plugin files, so use the other SortPlugins()
+  // overload to provide stubs.
+  const auto esm = GetPlugin(blankEsm);
+  const auto esp = GetPlugin(blankEsp);
+
+  esm->SetIsMaster(true);
+  esm->AddMaster(esp->GetName());
+
+  std::vector<PluginSortingData> pluginsSortingData{
+      CreatePluginSortingData(esm->GetName()),
+      CreatePluginSortingData(esp->GetName())};
+
+  try {
+    SortPlugins(std::move(pluginsSortingData), GetParam(), {Group()}, {}, {});
+    FAIL();
+  } catch (const CyclicInteractionError& e) {
+    ASSERT_EQ(2, e.GetCycle().size());
+    EXPECT_EQ(esp->GetName(), e.GetCycle()[0].GetName());
+    EXPECT_EQ(EdgeType::master, e.GetCycle()[0].GetTypeOfEdgeToNextVertex());
+    EXPECT_EQ(esm->GetName(), e.GetCycle()[1].GetName());
+    EXPECT_EQ(EdgeType::masterFlag,
+              e.GetCycle()[1].GetTypeOfEdgeToNextVertex());
+  }
+}
+
+TEST_P(
+    PluginSortTest,
+    sortingShouldThrowIfMasterlistRequirementEdgeWouldContradictMasterFlags) {
+  using std::endl;
+
+  ASSERT_NO_THROW(loadInstalledPlugins(game_, false));
+
+  const auto masterlistPath = metadataFilesPath / "masterlist.yaml";
+  std::ofstream masterlist(masterlistPath);
+  masterlist << "plugins:" << endl
+             << "  - name: " << blankEsm << endl
+             << "    req:" << endl
+             << "      - " << blankEsp << endl;
+  masterlist.close();
+
+  game_.GetDatabase().LoadLists(masterlistPath);
+
+  try {
+    SortPlugins(game_, game_.GetLoadOrder());
+    FAIL();
+  } catch (const CyclicInteractionError& e) {
+    ASSERT_EQ(2, e.GetCycle().size());
+    EXPECT_EQ(blankEsp, e.GetCycle()[0].GetName());
+    EXPECT_EQ(EdgeType::masterlistRequirement,
+              e.GetCycle()[0].GetTypeOfEdgeToNextVertex());
+    EXPECT_EQ(blankEsm, e.GetCycle()[1].GetName());
+    EXPECT_EQ(EdgeType::masterFlag,
+              e.GetCycle()[1].GetTypeOfEdgeToNextVertex());
+  }
+}
+
+TEST_P(PluginSortTest,
+       sortingShouldThrowIfUserRequirementEdgeWouldContradictMasterFlags) {
+  ASSERT_NO_THROW(loadInstalledPlugins(game_, false));
+
+  PluginMetadata plugin(blankEsm);
+  plugin.SetRequirements({File(blankEsp)});
+
+  game_.GetDatabase().SetPluginUserMetadata(plugin);
+
+  try {
+    SortPlugins(game_, game_.GetLoadOrder());
+    FAIL();
+  } catch (const CyclicInteractionError& e) {
+    ASSERT_EQ(2, e.GetCycle().size());
+    EXPECT_EQ(blankEsp, e.GetCycle()[0].GetName());
+    EXPECT_EQ(EdgeType::userRequirement,
+              e.GetCycle()[0].GetTypeOfEdgeToNextVertex());
+    EXPECT_EQ(blankEsm, e.GetCycle()[1].GetName());
+    EXPECT_EQ(EdgeType::masterFlag,
+              e.GetCycle()[1].GetTypeOfEdgeToNextVertex());
+  }
+}
+
+TEST_P(PluginSortTest,
+       sortingShouldThrowIfMasterlistLoadAfterEdgeWouldContradictMasterFlags) {
+  using std::endl;
+
+  ASSERT_NO_THROW(loadInstalledPlugins(game_, false));
+
+  const auto masterlistPath = metadataFilesPath / "masterlist.yaml";
+  std::ofstream masterlist(masterlistPath);
+  masterlist << "plugins:" << endl
+             << "  - name: " << blankEsm << endl
+             << "    after:" << endl
+             << "      - " << blankEsp << endl;
+  masterlist.close();
+
+  game_.GetDatabase().LoadLists(masterlistPath);
+
+  try {
+    SortPlugins(game_, game_.GetLoadOrder());
+    FAIL();
+  } catch (const CyclicInteractionError& e) {
+    ASSERT_EQ(2, e.GetCycle().size());
+    EXPECT_EQ(blankEsp, e.GetCycle()[0].GetName());
+    EXPECT_EQ(EdgeType::masterlistLoadAfter,
+              e.GetCycle()[0].GetTypeOfEdgeToNextVertex());
+    EXPECT_EQ(blankEsm, e.GetCycle()[1].GetName());
+    EXPECT_EQ(EdgeType::masterFlag,
+              e.GetCycle()[1].GetTypeOfEdgeToNextVertex());
+  }
+}
+
+TEST_P(PluginSortTest,
+       sortingShouldThrowIfUserLoadAfterEdgeWouldContradictMasterFlags) {
+  ASSERT_NO_THROW(loadInstalledPlugins(game_, false));
+
+  PluginMetadata plugin(blankEsm);
+  plugin.SetLoadAfterFiles({File(blankEsp)});
+
+  game_.GetDatabase().SetPluginUserMetadata(plugin);
+
+  try {
+    SortPlugins(game_, game_.GetLoadOrder());
+    FAIL();
+  } catch (const CyclicInteractionError& e) {
+    ASSERT_EQ(2, e.GetCycle().size());
+    EXPECT_EQ(blankEsp, e.GetCycle()[0].GetName());
+    EXPECT_EQ(EdgeType::userLoadAfter,
+              e.GetCycle()[0].GetTypeOfEdgeToNextVertex());
+    EXPECT_EQ(blankEsm, e.GetCycle()[1].GetName());
+    EXPECT_EQ(EdgeType::masterFlag,
+              e.GetCycle()[1].GetTypeOfEdgeToNextVertex());
+  }
+}
+
+TEST_P(PluginSortTest,
+       sortingShouldThrowIfHardcodedEdgeWouldContradictMasterFlags) {
+  // Can't test with the test plugin files, so use the other SortPlugins()
+  // overload to provide stubs.
+  const auto esm = GetPlugin(blankEsm);
+  const auto esp = GetPlugin(blankEsp);
+
+  esm->SetIsMaster(true);
+
+  std::vector<PluginSortingData> pluginsSortingData{
+      CreatePluginSortingData(esm->GetName()),
+      CreatePluginSortingData(esp->GetName())};
+
+  EXPECT_THROW(SortPlugins(std::move(pluginsSortingData),
+                           GetParam(),
+                           {Group()},
+                           {},
+                           {esp->GetName()}),
+               CyclicInteractionError);
+
+  try {
+    SortPlugins(std::move(pluginsSortingData),
+                GetParam(),
+                {Group()},
+                {},
+                {esp->GetName()});
+    FAIL();
+  } catch (const CyclicInteractionError& e) {
+    ASSERT_EQ(2, e.GetCycle().size());
+    EXPECT_EQ(blankEsp, e.GetCycle()[0].GetName());
+    EXPECT_EQ(EdgeType::hardcoded, e.GetCycle()[0].GetTypeOfEdgeToNextVertex());
+    EXPECT_EQ(blankEsm, e.GetCycle()[1].GetName());
+    EXPECT_EQ(EdgeType::masterFlag,
+              e.GetCycle()[1].GetTypeOfEdgeToNextVertex());
+  }
+}
 }
 }