diff --git a/llvm/lib/Bitcode/Writer/BitcodeWriter.cpp b/llvm/lib/Bitcode/Writer/BitcodeWriter.cpp
index eadef18..428bb11 100644
--- a/llvm/lib/Bitcode/Writer/BitcodeWriter.cpp
+++ b/llvm/lib/Bitcode/Writer/BitcodeWriter.cpp
@@ -316,7 +316,7 @@
 
   /// When writing a subset of the index for distributed backends, client
   /// provides a map of modules to the corresponding GUIDs/summaries to write.
-  std::map<std::string, GVSummaryMapTy> *ModuleToSummariesForIndex;
+  const std::map<std::string, GVSummaryMapTy> *ModuleToSummariesForIndex;
 
   /// Map that holds the correspondence between the GUID used in the combined
   /// index and a value id generated by this class to use in references.
@@ -331,7 +331,7 @@
   /// for a distributed backend, provide a \p ModuleToSummariesForIndex map.
   IndexBitcodeWriter(SmallVectorImpl<char> &Buffer,
                      const ModuleSummaryIndex &Index,
-                     std::map<std::string, GVSummaryMapTy>
+                     const std::map<std::string, GVSummaryMapTy>
                          *ModuleToSummariesForIndex = nullptr)
       : BitcodeWriter(Buffer), Index(Index),
         ModuleToSummariesForIndex(ModuleToSummariesForIndex) {
@@ -359,11 +359,11 @@
     // ModuleToSummariesForIndex map:
 
     /// Points to the last element in outer ModuleToSummariesForIndex map.
-    std::map<std::string, GVSummaryMapTy>::iterator ModuleSummariesBack;
+    std::map<std::string, GVSummaryMapTy>::const_iterator ModuleSummariesBack;
     /// Iterator on outer ModuleToSummariesForIndex map.
-    std::map<std::string, GVSummaryMapTy>::iterator ModuleSummariesIter;
+    std::map<std::string, GVSummaryMapTy>::const_iterator ModuleSummariesIter;
     /// Iterator on an inner global variable summary map.
-    GVSummaryMapTy::iterator ModuleGVSummariesIter;
+    GVSummaryMapTy::const_iterator ModuleGVSummariesIter;
 
     // Iterators used when writing all summaries in the index:
 
@@ -3840,7 +3840,7 @@
 // index for a distributed backend, provide a \p ModuleToSummariesForIndex map.
 void llvm::WriteIndexToFile(
     const ModuleSummaryIndex &Index, raw_ostream &Out,
-    std::map<std::string, GVSummaryMapTy> *ModuleToSummariesForIndex) {
+    const std::map<std::string, GVSummaryMapTy> *ModuleToSummariesForIndex) {
   SmallVector<char, 0> Buffer;
   Buffer.reserve(256 * 1024);