diff --git a/apps/opencs/model/tools/mergestages.cpp b/apps/opencs/model/tools/mergestages.cpp
index e11be72d4e..5a7fa6c1b9 100644
--- a/apps/opencs/model/tools/mergestages.cpp
+++ b/apps/opencs/model/tools/mergestages.cpp
@@ -15,7 +15,6 @@
 
 #include <components/esm3/cellref.hpp>
 #include <components/esm3/esmreader.hpp>
-#include <components/misc/strings/lower.hpp>
 
 #include "mergestate.hpp"
 
@@ -117,7 +116,7 @@ void CSMTools::MergeReferencesStage::perform(int stage, CSMDoc::Messages& messag
 
         ref.mOriginalCell = ref.mCell;
 
-        ref.mRefNum.mIndex = mIndex[Misc::StringUtils::lowerCase(ref.mCell.getRefIdString())]++;
+        ref.mRefNum.mIndex = mIndex[ref.mCell]++;
         ref.mRefNum.mContentFile = 0;
         ref.mNew = false;
 
diff --git a/apps/opencs/model/tools/mergestages.hpp b/apps/opencs/model/tools/mergestages.hpp
index 0763398e9d..42f06858b1 100644
--- a/apps/opencs/model/tools/mergestages.hpp
+++ b/apps/opencs/model/tools/mergestages.hpp
@@ -113,7 +113,7 @@ namespace CSMTools
     class MergeReferencesStage : public CSMDoc::Stage
     {
         MergeState& mState;
-        std::map<std::string, int> mIndex;
+        std::map<ESM::RefId, int> mIndex;
 
     public:
         MergeReferencesStage(MergeState& state);