diff --git a/include/clang/AST/DeclBase.h b/include/clang/AST/DeclBase.h
index 12f37e53e9..09e1fdcd63 100644
--- a/include/clang/AST/DeclBase.h
+++ b/include/clang/AST/DeclBase.h
@@ -532,6 +532,14 @@ public:
   /// a precompiled header or module) rather than having been parsed.
   bool isFromASTFile() const { return FromASTFile; }
 
+  /// \brief Retrieve the global declaration ID associated with this 
+  /// declaration, which specifies where in the 
+  unsigned getGlobalID() const { 
+    if (isFromASTFile())
+      return *((const unsigned*)this - 1);
+    return 0;
+  }
+              
   unsigned getIdentifierNamespace() const {
     return IdentifierNamespace;
   }
diff --git a/include/clang/Serialization/ASTReader.h b/include/clang/Serialization/ASTReader.h
index f808b962e1..4a704d0c35 100644
--- a/include/clang/Serialization/ASTReader.h
+++ b/include/clang/Serialization/ASTReader.h
@@ -675,13 +675,6 @@ private:
   /// \brief Keeps track of the elements added to PendingDeclChains.
   llvm::SmallSet<serialization::DeclID, 16> PendingDeclChainsKnown;
 
-  /// \brief Reverse mapping from declarations to their global declaration IDs.
-  /// 
-  /// FIXME: This data structure is currently only used for ObjCInterfaceDecls
-  /// and ObjCProtocolDecls to support declaration merging. If we must have 
-  /// this for other declarations, allocate it along with the Decl itself.
-  llvm::DenseMap<Decl *, serialization::GlobalDeclID> DeclToID;
-  
   typedef llvm::DenseMap<Decl *, llvm::SmallVector<serialization::DeclID, 2> >
     MergedDeclsMap;
     
diff --git a/lib/AST/DeclBase.cpp b/lib/AST/DeclBase.cpp
index 55484188c8..f4e5d43ee6 100644
--- a/lib/AST/DeclBase.cpp
+++ b/lib/AST/DeclBase.cpp
@@ -44,7 +44,20 @@ static bool StatSwitch = false;
 void *Decl::AllocateDeserializedDecl(const ASTContext &Context, 
                                      unsigned ID,
                                      unsigned Size) {
-  return Context.Allocate(Size);
+  // Allocate an extra pointer's worth of storage, which ensures that 
+  //   (1) We have enough storage to stash the global declaration ID, and
+  //   (2) We maintain pointer alignment.
+  //
+  // Note that this wastes 4 bytes on x86-64, which we'll undoubtedly end up
+  // finding a use for later.
+  void *Start = Context.Allocate(Size + sizeof(void*));
+  void *Result = (char*)Start + sizeof(void*);
+  
+  // Store the global declaration ID 
+  unsigned *IDPtr = (unsigned*)Result - 1;
+  *IDPtr = ID;
+  
+  return Result;
 }
 
 const char *Decl::getDeclKindName() const {
diff --git a/lib/Serialization/ASTReaderDecl.cpp b/lib/Serialization/ASTReaderDecl.cpp
index cff8667f4b..0672129f1e 100644
--- a/lib/Serialization/ASTReaderDecl.cpp
+++ b/lib/Serialization/ASTReaderDecl.cpp
@@ -402,9 +402,6 @@ void ASTDeclReader::VisitTypeDecl(TypeDecl *TD) {
 }
 
 void ASTDeclReader::VisitTypedefNameDecl(TypedefNameDecl *TD) {
-  // Record the declaration -> global ID mapping.
-  Reader.DeclToID[TD] = ThisDeclID;
-  
   RedeclarableResult Redecl = VisitRedeclarable(TD);
   VisitTypeDecl(TD);
   
@@ -421,9 +418,6 @@ void ASTDeclReader::VisitTypeAliasDecl(TypeAliasDecl *TD) {
 }
 
 void ASTDeclReader::VisitTagDecl(TagDecl *TD) {
-  // Record the declaration -> global ID mapping.
-  Reader.DeclToID[TD] = ThisDeclID;
-    
   RedeclarableResult Redecl = VisitRedeclarable(TD);
   VisitTypeDecl(TD);
   
@@ -490,9 +484,6 @@ void ASTDeclReader::VisitDeclaratorDecl(DeclaratorDecl *DD) {
 }
 
 void ASTDeclReader::VisitFunctionDecl(FunctionDecl *FD) {
-  // Record the declaration -> global ID mapping.
-  Reader.DeclToID[FD] = ThisDeclID;
-  
   RedeclarableResult Redecl = VisitRedeclarable(FD);
   VisitDeclaratorDecl(FD);
 
@@ -673,9 +664,6 @@ void ASTDeclReader::VisitObjCContainerDecl(ObjCContainerDecl *CD) {
 }
 
 void ASTDeclReader::VisitObjCInterfaceDecl(ObjCInterfaceDecl *ID) {
-  // Record the declaration -> global ID mapping.
-  Reader.DeclToID[ID] = ThisDeclID;
-  
   RedeclarableResult Redecl = VisitRedeclarable(ID);
   VisitObjCContainerDecl(ID);
   TypeIDForTypeDecl = Reader.getGlobalTypeID(F, Record[Idx++]);
@@ -746,9 +734,6 @@ void ASTDeclReader::VisitObjCIvarDecl(ObjCIvarDecl *IVD) {
 }
 
 void ASTDeclReader::VisitObjCProtocolDecl(ObjCProtocolDecl *PD) {
-  // Record the declaration -> global ID mapping.
-  Reader.DeclToID[PD] = ThisDeclID;
-  
   RedeclarableResult Redecl = VisitRedeclarable(PD);
   VisitObjCContainerDecl(PD);
   mergeRedeclarable(PD, Redecl);
@@ -880,9 +865,6 @@ void ASTDeclReader::VisitIndirectFieldDecl(IndirectFieldDecl *FD) {
 }
 
 void ASTDeclReader::VisitVarDecl(VarDecl *VD) {
-  // Record the declaration -> global ID mapping.
-  Reader.DeclToID[VD] = ThisDeclID;
-  
   RedeclarableResult Redecl = VisitRedeclarable(VD);
   VisitDeclaratorDecl(VD);
   
@@ -1561,7 +1543,7 @@ void ASTDeclReader::mergeRedeclarable(Redeclarable<T> *D,
         // Introduce ExistingCanon into the set of pending declaration chains,
         // if in fact it came from a module file.
         if (ExistingCanon->isFromASTFile()) {
-          GlobalDeclID ExistingCanonID = Reader.DeclToID[ExistingCanon];
+          GlobalDeclID ExistingCanonID = ExistingCanon->getGlobalID();
           assert(ExistingCanonID && "Unrecorded canonical declaration ID?");
           if (Reader.PendingDeclChainsKnown.insert(ExistingCanonID))
             Reader.PendingDeclChains.push_back(ExistingCanonID);
diff --git a/lib/Serialization/ASTWriter.cpp b/lib/Serialization/ASTWriter.cpp
index 1317525c27..52578599ea 100644
--- a/lib/Serialization/ASTWriter.cpp
+++ b/lib/Serialization/ASTWriter.cpp
@@ -2914,7 +2914,7 @@ void ASTWriter::WriteMergedDecls() {
   for (ASTReader::MergedDeclsMap::iterator I = Chain->MergedDecls.begin(),
                                         IEnd = Chain->MergedDecls.end();
        I != IEnd; ++I) {
-    DeclID CanonID = I->first->isFromASTFile()? Chain->DeclToID[I->first]
+    DeclID CanonID = I->first->isFromASTFile()? I->first->getGlobalID()
                                               : getDeclID(I->first);
     assert(CanonID && "Merged declaration not known?");