diff --git a/lib/Frontend/PCHReader.cpp b/lib/Frontend/PCHReader.cpp
index 2252fd4..7229775 100644
--- a/lib/Frontend/PCHReader.cpp
+++ b/lib/Frontend/PCHReader.cpp
@@ -1642,6 +1642,15 @@
                                  Record.begin(), Record.end());
       break;
 
+    case pch::WEAK_UNDECLARED_IDENTIFIERS:
+      // Optimization for the first block.
+      if (WeakUndeclaredIdentifiers.empty())
+        WeakUndeclaredIdentifiers.swap(Record);
+      else
+        WeakUndeclaredIdentifiers.insert(WeakUndeclaredIdentifiers.end(),
+                                         Record.begin(), Record.end());
+      break;
+
     case pch::LOCALLY_SCOPED_EXTERNAL_DECLS:
       // Optimization for the first block.
       if (LocallyScopedExternalDecls.empty())
@@ -3131,6 +3140,21 @@
     SemaObj->UnusedStaticFuncs.push_back(FD);
   }
 
+  // If there were any weak undeclared identifiers, deserialize them and add to
+  // Sema's list of weak undeclared identifiers.
+  if (!WeakUndeclaredIdentifiers.empty()) {
+    unsigned Idx = 0;
+    for (unsigned I = 0, N = WeakUndeclaredIdentifiers[Idx++]; I != N; ++I) {
+      IdentifierInfo *WeakId = GetIdentifierInfo(WeakUndeclaredIdentifiers,Idx);
+      IdentifierInfo *AliasId=GetIdentifierInfo(WeakUndeclaredIdentifiers,Idx);
+      SourceLocation Loc = ReadSourceLocation(WeakUndeclaredIdentifiers, Idx);
+      bool Used = WeakUndeclaredIdentifiers[Idx++];
+      Sema::WeakInfo WI(AliasId, Loc);
+      WI.setUsed(Used);
+      SemaObj->WeakUndeclaredIdentifiers.insert(std::make_pair(WeakId, WI));
+    }
+  }
+
   // If there were any locally-scoped external declarations,
   // deserialize them and add them to Sema's table of locally-scoped
   // external declarations.
diff --git a/lib/Frontend/PCHWriter.cpp b/lib/Frontend/PCHWriter.cpp
index b2fd984..d6dc36f 100644
--- a/lib/Frontend/PCHWriter.cpp
+++ b/lib/Frontend/PCHWriter.cpp
@@ -2207,6 +2207,20 @@
   RecordData UnusedStaticFuncs;
   for (unsigned i=0, e = SemaRef.UnusedStaticFuncs.size(); i !=e; ++i)
     AddDeclRef(SemaRef.UnusedStaticFuncs[i], UnusedStaticFuncs);
+  
+  RecordData WeakUndeclaredIdentifiers;
+  if (!SemaRef.WeakUndeclaredIdentifiers.empty()) {
+    WeakUndeclaredIdentifiers.push_back(
+                                      SemaRef.WeakUndeclaredIdentifiers.size());
+    for (llvm::DenseMap<IdentifierInfo*,Sema::WeakInfo>::iterator
+         I = SemaRef.WeakUndeclaredIdentifiers.begin(),
+         E = SemaRef.WeakUndeclaredIdentifiers.end(); I != E; ++I) {
+      AddIdentifierRef(I->first, WeakUndeclaredIdentifiers);
+      AddIdentifierRef(I->second.getAlias(), WeakUndeclaredIdentifiers);
+      AddSourceLocation(I->second.getLocation(), WeakUndeclaredIdentifiers);
+      WeakUndeclaredIdentifiers.push_back(I->second.getUsed());
+    }
+  }
 
   // Build a record containing all of the locally-scoped external
   // declarations in this header file. Generally, this record will be
@@ -2311,6 +2325,11 @@
   if (!UnusedStaticFuncs.empty())
     Stream.EmitRecord(pch::UNUSED_STATIC_FUNCS, UnusedStaticFuncs);
 
+  // Write the record containing weak undeclared identifiers.
+  if (!WeakUndeclaredIdentifiers.empty())
+    Stream.EmitRecord(pch::WEAK_UNDECLARED_IDENTIFIERS,
+                      WeakUndeclaredIdentifiers);
+
   // Write the record containing locally-scoped external definitions.
   if (!LocallyScopedExternalDecls.empty())
     Stream.EmitRecord(pch::LOCALLY_SCOPED_EXTERNAL_DECLS,