diff --git a/include/llvm/ADT/PointerUnion.h b/include/llvm/ADT/PointerUnion.h
index 8cbe8d1df75..dafd0e05109 100644
--- a/include/llvm/ADT/PointerUnion.h
+++ b/include/llvm/ADT/PointerUnion.h
@@ -15,6 +15,7 @@
 #ifndef LLVM_ADT_POINTERUNION_H
 #define LLVM_ADT_POINTERUNION_H
 
+#include "llvm/ADT/DenseMapInfo.h"
 #include "llvm/ADT/PointerIntPair.h"
 #include "llvm/Support/Compiler.h"
 
@@ -455,6 +456,33 @@ namespace llvm {
           ::NumLowBitsAvailable
     };
   };
+
+  // Teach DenseMap how to use PointerUnions as keys.
+  template<typename T, typename U>
+  struct DenseMapInfo<PointerUnion<T, U> > {
+    typedef PointerUnion<T, U> Pair;
+    typedef DenseMapInfo<T> FirstInfo;
+    typedef DenseMapInfo<U> SecondInfo;
+
+    static inline Pair getEmptyKey() {
+      return Pair(FirstInfo::getEmptyKey());
+    }
+    static inline Pair getTombstoneKey() {
+      return Pair(FirstInfo::getTombstoneKey());
+    }
+    static unsigned getHashValue(const Pair &PairVal) {
+      intptr_t key = (intptr_t)PairVal.getOpaqueValue();
+      return DenseMapInfo<intptr_t>::getHashValue(key);
+    }
+    static bool isEqual(const Pair &LHS, const Pair &RHS) {
+      return LHS.template is<T>() == RHS.template is<T>() &&
+             (LHS.template is<T>() ?
+              FirstInfo::isEqual(LHS.template get<T>(),
+                                 RHS.template get<T>()) :
+              SecondInfo::isEqual(LHS.template get<U>(),
+                                  RHS.template get<U>()));
+    }
+  };
 }
 
 #endif