diff --git a/apps/openmw/mwworld/esmstore.cpp b/apps/openmw/mwworld/esmstore.cpp
index d366a5a68..1f6ed5102 100644
--- a/apps/openmw/mwworld/esmstore.cpp
+++ b/apps/openmw/mwworld/esmstore.cpp
@@ -45,7 +45,7 @@ void ESMStore::load(ESM::ESMReader &esm, Loading::Listener* listener)
     const std::vector<ESM::Header::MasterData> &masters = esm.getGameFiles();
     std::vector<ESM::ESMReader> *allPlugins = esm.getGlobalReaderList();
     for (size_t j = 0; j < masters.size(); j++) {
-        ESM::Header::MasterData &mast = const_cast<ESM::Header::MasterData&>(masters[j]);
+        const ESM::Header::MasterData &mast = masters[j];
         std::string fname = mast.name;
         int index = ~0;
         for (int i = 0; i < esm.getIndex(); i++) {
@@ -63,7 +63,7 @@ void ESMStore::load(ESM::ESMReader &esm, Loading::Listener* listener)
                 + ", but it has not been loaded yet. Please check your load order.";
             esm.fail(fstring);
         }
-        mast.index = index;
+        esm.addParentFileIndex(index);
     }
 
     // Loop through all records
diff --git a/components/esm/esmcommon.hpp b/components/esm/esmcommon.hpp
index 97ce88556..f7a8bf126 100644
--- a/components/esm/esmcommon.hpp
+++ b/components/esm/esmcommon.hpp
@@ -3,6 +3,7 @@
 
 #include <string>
 #include <cstring>
+#include <vector>
 
 #include <stdint.h>
 #include <string.h>
@@ -126,6 +127,7 @@ struct ESM_Context
   //  actually contribute to a specific cell. Therefore, we need to store the index
   //  of the file belonging to this contest. See CellStore::(list/load)refs for details.
   int index;
+  std::vector<int> parentFileIndices;
 
   // True if subName has been read but not used.
   bool subCached;
diff --git a/components/esm/esmreader.cpp b/components/esm/esmreader.cpp
index 92dbba167..1b6eca734 100644
--- a/components/esm/esmreader.cpp
+++ b/components/esm/esmreader.cpp
@@ -20,8 +20,7 @@ ESM_Context ESMReader::getContext()
 }
 
 ESMReader::ESMReader()
-    : mIdx(0)
-    , mRecordFlags(0)
+    : mRecordFlags(0)
     , mBuffer(50*1024)
     , mGlobalReaderList(nullptr)
     , mEncoder(nullptr)
diff --git a/components/esm/esmreader.hpp b/components/esm/esmreader.hpp
index 72a7b4790..761756e8f 100644
--- a/components/esm/esmreader.hpp
+++ b/components/esm/esmreader.hpp
@@ -79,13 +79,15 @@ public:
   //  terrain palette, but ESMReader does not pass a reference to the correct plugin
   //  to the individual load() methods. This hack allows to pass this reference
   //  indirectly to the load() method.
-  int mIdx;
-  void setIndex(const int index) {mIdx = index; mCtx.index = index;}
-  int getIndex() {return mIdx;}
+  void setIndex(const int index) { mCtx.index = index;}
+  int getIndex() {return mCtx.index;}
 
   void setGlobalReaderList(std::vector<ESMReader> *list) {mGlobalReaderList = list;}
   std::vector<ESMReader> *getGlobalReaderList() {return mGlobalReaderList;}
 
+  void addParentFileIndex(int index) { mCtx.parentFileIndices.push_back(index); }
+  const std::vector<int>& getParentFileIndices() const { return mCtx.parentFileIndices; }
+
   /*************************************************************************
    *
    *  Medium-level reading shortcuts
diff --git a/components/esm/loadcell.cpp b/components/esm/loadcell.cpp
index 5b259acef..f92a752a4 100644
--- a/components/esm/loadcell.cpp
+++ b/components/esm/loadcell.cpp
@@ -21,12 +21,12 @@ namespace
 
         // If we have an index value that does not make sense, assume that it was an addition
         // by the present plugin (but a faulty one)
-        if (local && local <= reader.getGameFiles().size())
+        if (local && local <= reader.getParentFileIndices().size())
         {
             // If the most significant 8 bits are used, then this reference already exists.
             // In this case, do not spawn a new reference, but overwrite the old one.
             refNum.mIndex &= 0x00ffffff; // delete old plugin ID
-            refNum.mContentFile = reader.getGameFiles()[local-1].index;
+            refNum.mContentFile = reader.getParentFileIndices()[local-1];
         }
         else
         {