diff --git a/lib/Bitcode/Reader/BitcodeReader.cpp b/lib/Bitcode/Reader/BitcodeReader.cpp
index a328837..b9453c9 100644
--- a/lib/Bitcode/Reader/BitcodeReader.cpp
+++ b/lib/Bitcode/Reader/BitcodeReader.cpp
@@ -293,6 +293,8 @@
       } else if (ConstantStruct *UserCS = dyn_cast<ConstantStruct>(UserC)) {
         NewC = ConstantStruct::get(Context, &NewOps[0], NewOps.size(),
                                          UserCS->getType()->isPacked());
+      } else if (ConstantUnion *UserCU = dyn_cast<ConstantUnion>(UserC)) {
+        NewC = ConstantUnion::get(UserCU->getType(), NewOps[0]);
       } else if (isa<ConstantVector>(UserC)) {
         NewC = ConstantVector::get(&NewOps[0], NewOps.size());
       } else {
@@ -1015,6 +1017,11 @@
           Elts.push_back(ValueList.getConstantFwdRef(Record[i],
                                                      STy->getElementType(i)));
         V = ConstantStruct::get(STy, Elts);
+      } else if (const UnionType *UnTy = dyn_cast<UnionType>(CurTy)) {
+        uint64_t Index = Record[0];
+        Constant *Val = ValueList.getConstantFwdRef(Record[1],
+                                        UnTy->getElementType(Index));
+        V = ConstantUnion::get(UnTy, Val);
       } else if (const ArrayType *ATy = dyn_cast<ArrayType>(CurTy)) {
         const Type *EltTy = ATy->getElementType();
         for (unsigned i = 0; i != Size; ++i)
diff --git a/lib/Bitcode/Writer/BitcodeWriter.cpp b/lib/Bitcode/Writer/BitcodeWriter.cpp
index 82e73b5..3ab2726 100644
--- a/lib/Bitcode/Writer/BitcodeWriter.cpp
+++ b/lib/Bitcode/Writer/BitcodeWriter.cpp
@@ -808,11 +808,25 @@
       else if (isCStr7)
         AbbrevToUse = CString7Abbrev;
     } else if (isa<ConstantArray>(C) || isa<ConstantStruct>(V) ||
-               isa<ConstantUnion>(C) || isa<ConstantVector>(V)) {
+               isa<ConstantVector>(V)) {
       Code = bitc::CST_CODE_AGGREGATE;
       for (unsigned i = 0, e = C->getNumOperands(); i != e; ++i)
         Record.push_back(VE.getValueID(C->getOperand(i)));
       AbbrevToUse = AggregateAbbrev;
+    } else if (isa<ConstantUnion>(C)) {
+      Code = bitc::CST_CODE_AGGREGATE;
+
+      // Unions only have one entry but we must send type along with it.
+      const Type *EntryKind = C->getOperand(0)->getType();
+
+      const UnionType *UnTy = cast<UnionType>(C->getType());
+      int UnionIndex = UnTy->getElementTypeIndex(EntryKind);
+      assert(UnionIndex != -1 && "Constant union contains invalid entry");
+
+      Record.push_back(UnionIndex);
+      Record.push_back(VE.getValueID(C->getOperand(0)));
+
+      AbbrevToUse = AggregateAbbrev;
     } else if (const ConstantExpr *CE = dyn_cast<ConstantExpr>(C)) {
       switch (CE->getOpcode()) {
       default: