diff --git a/llvm/include/llvm/IR/ModuleSummaryIndex.h b/llvm/include/llvm/IR/ModuleSummaryIndex.h
index 395c9e332eb8f..d5ff15063671d 100644
--- a/llvm/include/llvm/IR/ModuleSummaryIndex.h
+++ b/llvm/include/llvm/IR/ModuleSummaryIndex.h
@@ -1377,7 +1377,7 @@ class ModuleSummaryIndex {
 
   // Temporary map while building StackIds list. Clear when index is completely
   // built via releaseTemporaryMemory.
-  std::map<uint64_t, unsigned> StackIdToIndex;
+  DenseMap<uint64_t, unsigned> StackIdToIndex;
 
   // YAML I/O support.
   friend yaml::MappingTraits<ModuleSummaryIndex>;