diff --git a/distribution/changelog.txt b/distribution/changelog.txt
index 5071ba2467..0dacff9933 100644
--- a/distribution/changelog.txt
+++ b/distribution/changelog.txt
@@ -4,6 +4,7 @@
 - Improved: [#21753] Tracked rides with cheated powered launch mode can change powered launch speed without extra cheats.
 - Improved: [#25941] The command line sprite build command is now faster.
 - Fix: [#14686, #23996, #25981] Preview images from different windows overwrite each other when using OpenGL.
+- Fix: [#15128, #15626, #16331, #17443, #18626, #21597, #24175, #24971, #25963] Crash when loading corrupted RCT2/RCT1 save files with duplicate entity indices.
 - Fix: [#25237] Wrong colours on the Knight costume.
 - Fix: [#25712, #25727] Crash during startup from window list race condition.
 - Fix: [#25910] Folders starting with numbers are sorted incorrectly (e.g. 1, 10, 2 instead of 1, 2, 10).
diff --git a/src/openrct2/rct1/S4Importer.cpp b/src/openrct2/rct1/S4Importer.cpp
index 1fb200a892..b33ff0a31e 100644
--- a/src/openrct2/rct1/S4Importer.cpp
+++ b/src/openrct2/rct1/S4Importer.cpp
@@ -1245,6 +1245,9 @@ namespace OpenRCT2::RCT1
         {
             for (int i = 0; i < Limits::kMaxEntities; i++)
             {
+                // Make sure the EntityIndex matches the array position to handle corrupted saves where duplicate or invalid
+                // indices would cause CreateEntityAt to fail
+                _s4.Entities[i].Unknown.EntityIndex = static_cast<uint16_t>(i);
                 ImportEntity(gameState, _s4.Entities[i].Unknown);
             }
         }
diff --git a/src/openrct2/rct2/S6Importer.cpp b/src/openrct2/rct2/S6Importer.cpp
index fad4138650..fde0182e56 100644
--- a/src/openrct2/rct2/S6Importer.cpp
+++ b/src/openrct2/rct2/S6Importer.cpp
@@ -1651,6 +1651,9 @@ namespace OpenRCT2::RCT2
         {
             for (int32_t i = 0; i < GetMaxEntities(); i++)
             {
+                // Make sure the EntityIndex matches the array position to handle corrupted saves where duplicate or invalid
+                // indices would cause CreateEntityAt to fail
+                _s6.Entities[i].Unknown.EntityIndex = static_cast<uint16_t>(i);
                 ImportEntity(gameState, _s6.Entities[i].Unknown);
             }
         }
diff --git a/test/tests/CMakeLists.txt b/test/tests/CMakeLists.txt
index 707bdf0434..483a54d1a5 100644
--- a/test/tests/CMakeLists.txt
+++ b/test/tests/CMakeLists.txt
@@ -26,6 +26,7 @@ set(test_files
    "${CMAKE_CURRENT_SOURCE_DIR}/PlayTests.cpp"
    "${CMAKE_CURRENT_SOURCE_DIR}/ReplayTests.cpp"
    "${CMAKE_CURRENT_SOURCE_DIR}/RideRatings.cpp"
+   "${CMAKE_CURRENT_SOURCE_DIR}/EntityImportTests.cpp"
    "${CMAKE_CURRENT_SOURCE_DIR}/S6ImportExportTests.cpp"
    "${CMAKE_CURRENT_SOURCE_DIR}/SawyerCodingTest.cpp"
    "${CMAKE_CURRENT_SOURCE_DIR}/ScenarioPatcherTests.cpp"
diff --git a/test/tests/EntityImportTests.cpp b/test/tests/EntityImportTests.cpp
new file mode 100644
index 0000000000..fabdbabc35
--- /dev/null
+++ b/test/tests/EntityImportTests.cpp
@@ -0,0 +1,79 @@
+/*****************************************************************************
+ * Copyright (c) 2014-2026 OpenRCT2 developers
+ *
+ * For a complete list of all authors, please refer to contributors.md
+ * Interested in contributing? Visit https://github.com/OpenRCT2/OpenRCT2
+ *
+ * OpenRCT2 is licensed under the GNU General Public License version 3.
+ *****************************************************************************/
+
+#include "TestData.h"
+
+#include <gtest/gtest.h>
+#include <openrct2/Context.h>
+#include <openrct2/GameState.h>
+#include <openrct2/OpenRCT2.h>
+#include <openrct2/ParkImporter.h>
+#include <openrct2/core/FileStream.h>
+#include <openrct2/entity/EntityRegistry.h>
+#include <openrct2/entity/Guest.h>
+#include <openrct2/object/ObjectManager.h>
+#include <openrct2/world/MapAnimation.h>
+
+using namespace OpenRCT2;
+
+class EntityImportTests : public testing::Test
+{
+protected:
+    std::unique_ptr<IContext> context;
+
+    void SetUp() override
+    {
+        gOpenRCT2Headless = true;
+        gOpenRCT2NoGraphics = true;
+        context = CreateContext();
+        ASSERT_NE(context, nullptr);
+        ASSERT_TRUE(context->Initialise());
+    }
+
+    void TearDown() override
+    {
+        context.reset();
+    }
+};
+
+// This here tests that CreateEntityAt returns nullptr when trying to create an entity at an index that's already occupied.
+// This behavior is what caused crashes before, corrupted saves had duplicate EntityIndex values that caused CreateEntityAt to
+// return nullptr, which was then dereferenced.
+TEST_F(EntityImportTests, CreateEntityAtDuplicateIndexReturnsNull)
+{
+    auto& gameState = getGameState();
+    gameState.entities.ResetAllEntities();
+
+    // Create an entity at index 100
+    auto* entity1 = gameState.entities.CreateEntityAt<Guest>(EntityId::FromUnderlying(100));
+    ASSERT_NE(entity1, nullptr);
+    EXPECT_EQ(entity1->Id.ToUnderlying(), 100u);
+
+    // Try to create another entity at the same index, which should return nullptr
+    auto* entity2 = gameState.entities.CreateEntityAt<Guest>(EntityId::FromUnderlying(100));
+    EXPECT_EQ(entity2, nullptr);
+}
+
+// This test verifies that corrupted S6 files with duplicate EntityIndex values can be loaded without crashing.
+TEST_F(EntityImportTests, S6ImportCorruptedDuplicateEntityIndicesDoesNotCrash)
+{
+    std::string testParkPath = TestData::GetParkPath("corrupted_duplicate_entity_indices.sv6");
+    auto fs = FileStream(testParkPath, FileMode::open);
+
+    auto& objManager = context->GetObjectManager();
+    auto importer = ParkImporter::CreateS6(context->GetObjectRepository());
+    auto loadResult = importer->LoadFromStream(&fs, false);
+    objManager.LoadObjects(loadResult.RequiredObjects);
+
+    MapAnimations::ClearAll();
+    auto& gameState = getGameState();
+
+    // This should not crash because the code should sanitize EntityIndex values before CreateEntityAt is called
+    EXPECT_NO_THROW(importer->Import(gameState));
+}
diff --git a/test/tests/testdata/parks/corrupted_duplicate_entity_indices.sv6 b/test/tests/testdata/parks/corrupted_duplicate_entity_indices.sv6
new file mode 100644
index 0000000000..46e72a87da
Binary files /dev/null and b/test/tests/testdata/parks/corrupted_duplicate_entity_indices.sv6 differ
diff --git a/test/tests/tests.vcxproj b/test/tests/tests.vcxproj
index c79eab00b2..40cb31d587 100644
--- a/test/tests/tests.vcxproj
+++ b/test/tests/tests.vcxproj
@@ -95,6 +95,7 @@
     <ClCompile Include="PlayTests.cpp" />
     <ClCompile Include="Pathfinding.cpp" />
     <ClCompile Include="RideRatings.cpp" />
+    <ClCompile Include="EntityImportTests.cpp" />
     <ClCompile Include="S6ImportExportTests.cpp" />
     <ClCompile Include="SawyerCodingTest.cpp" />
     <ClCompile Include="ScenarioPatcherTests.cpp" />