diff --git a/distribution/changelog.txt b/distribution/changelog.txt
index 858edf9a6b..b91b1ad1b3 100644
--- a/distribution/changelog.txt
+++ b/distribution/changelog.txt
@@ -6,6 +6,7 @@
 - Feature: [#6235] Add drawing debug option for showing visuals when and where blocks of the screen are painted.
 - Feature: [#6292] Allow building queue lines in the Scenario Editor.
 - Feature: [#6325] Allow using g1.dat from RCT Classic.
+- Feature: [#6353] Show custom RCT1 scenarios in New Scenario window.
 - Feature: Allow using object files from RCT Classic.
 - Fix: [#816] In the map window, there are more peeps flickering than there are selected (original bug).
 - Fix: [#1833, #4937, #6138] 'Too low!' warning when building rides and shops on the lowest land level (original bug).
diff --git a/src/openrct2/rct1/S4Importer.cpp b/src/openrct2/rct1/S4Importer.cpp
index e4f25e82a9..e13b5a55a3 100644
--- a/src/openrct2/rct1/S4Importer.cpp
+++ b/src/openrct2/rct1/S4Importer.cpp
@@ -237,48 +237,53 @@ public:
 
     bool GetDetails(scenario_index_entry * dst) override
     {
-        bool result = false;
         Memory::Set(dst, 0, sizeof(scenario_index_entry));
 
         source_desc desc;
-        if (ScenarioSources::TryGetById(_s4.scenario_slot_index, &desc))
+        // If no entry is found, this is a custom scenario.
+        bool isOfficial = ScenarioSources::TryGetById(_s4.scenario_slot_index, &desc);
+
+        dst->category = desc.category;
+        dst->source_game = desc.source;
+        dst->source_index = desc.index;
+        dst->sc_id = desc.id;
+
+        dst->objective_type = _s4.scenario_objective_type;
+        dst->objective_arg_1 = _s4.scenario_objective_years;
+        // RCT1 used another way of calculating park value.
+        if (_s4.scenario_objective_type == OBJECTIVE_PARK_VALUE_BY)
+            dst->objective_arg_2 = CorrectRCT1ParkValue(_s4.scenario_objective_currency);
+        else
+            dst->objective_arg_2 = _s4.scenario_objective_currency;
+        dst->objective_arg_3 = _s4.scenario_objective_num_guests;
+
+        std::string name = std::string(_s4.scenario_name, sizeof(_s4.scenario_name));
+        std::string details;
+
+        // TryGetById won't set this property if the scenario is not recognised,
+        // but localisation needs it.
+        if (!isOfficial)
         {
-            dst->category = desc.category;
-            dst->source_game = desc.source;
-            dst->source_index = desc.index;
-            dst->sc_id = desc.id;
-
-            dst->objective_type = _s4.scenario_objective_type;
-            dst->objective_arg_1 = _s4.scenario_objective_years;
-            // RCT1 used another way of calculating park value.
-            if (_s4.scenario_objective_type == OBJECTIVE_PARK_VALUE_BY)
-                dst->objective_arg_2 = CorrectRCT1ParkValue(_s4.scenario_objective_currency);
-            else
-                dst->objective_arg_2 = _s4.scenario_objective_currency;
-            dst->objective_arg_3 = _s4.scenario_objective_num_guests;
-
-            std::string name = std::string(_s4.scenario_name, sizeof(_s4.scenario_name));
-            std::string details;
-            rct_string_id localisedStringIds[3];
-            if (language_get_localised_scenario_strings(desc.title, localisedStringIds))
-            {
-                if (localisedStringIds[0] != STR_NONE)
-                {
-                    name = String::ToStd(language_get_string(localisedStringIds[0]));
-                }
-                if (localisedStringIds[2] != STR_NONE)
-                {
-                    details = String::ToStd(language_get_string(localisedStringIds[2]));
-                }
-            }
-
-            String::Set(dst->name, sizeof(dst->name), name.c_str());
-            String::Set(dst->details, sizeof(dst->details), details.c_str());
-
-            result = true;
+            desc.title = name.c_str();
         }
 
-        return result;
+        rct_string_id localisedStringIds[3];
+        if (language_get_localised_scenario_strings(desc.title, localisedStringIds))
+        {
+            if (localisedStringIds[0] != STR_NONE)
+            {
+                name = String::ToStd(language_get_string(localisedStringIds[0]));
+            }
+            if (localisedStringIds[2] != STR_NONE)
+            {
+                details = String::ToStd(language_get_string(localisedStringIds[2]));
+            }
+        }
+
+        String::Set(dst->name, sizeof(dst->name), name.c_str());
+        String::Set(dst->details, sizeof(dst->details), details.c_str());
+
+        return true;
     }
 
     sint32 CorrectRCT1ParkValue(money32 oldParkValue)
diff --git a/src/openrct2/scenario/ScenarioRepository.cpp b/src/openrct2/scenario/ScenarioRepository.cpp
index 96fd7d6dfc..efce36d9d2 100644
--- a/src/openrct2/scenario/ScenarioRepository.cpp
+++ b/src/openrct2/scenario/ScenarioRepository.cpp
@@ -460,28 +460,36 @@ private:
     void AddScenario(const scenario_index_entry &entry)
     {
         auto filename = Path::GetFileName(entry.path);
-        auto existingEntry = GetByFilename(filename);
-        if (existingEntry != nullptr)
-        {
-            std::string conflictPath;
-            if (existingEntry->timestamp > entry.timestamp)
-            {
-                // Existing entry is more recent
-                conflictPath = String::ToStd(existingEntry->path);
 
-                // Overwrite existing entry with this one
-                *existingEntry = entry;
+        if (!String::Equals(filename, ""))
+        {
+            auto existingEntry = GetByFilename(filename);
+            if (existingEntry != nullptr)
+            {
+                std::string conflictPath;
+                if (existingEntry->timestamp > entry.timestamp)
+                {
+                    // Existing entry is more recent
+                    conflictPath = String::ToStd(existingEntry->path);
+
+                    // Overwrite existing entry with this one
+                    *existingEntry = entry;
+                }
+                else
+                {
+                    // This entry is more recent
+                    conflictPath = entry.path;
+                }
+                Console::WriteLine("Scenario conflict: '%s' ignored because it is newer.", conflictPath.c_str());
             }
             else
             {
-                // This entry is more recent
-                conflictPath = entry.path;
+                _scenarios.push_back(entry);
             }
-            Console::WriteLine("Scenario conflict: '%s' ignored because it is newer.", conflictPath.c_str());
         }
         else
         {
-            _scenarios.push_back(entry);
+            log_error("Tried to add scenario with an empty filename!");
         }
     }