diff --git a/lib/AST/DeclCXX.cpp b/lib/AST/DeclCXX.cpp
index 19caae5..78b15ff 100644
--- a/lib/AST/DeclCXX.cpp
+++ b/lib/AST/DeclCXX.cpp
@@ -363,6 +363,13 @@
   }
   
   if (D->isImplicit()) {
+    // Notify the serializer that an implicit member changed the definition.
+    // A chained PCH will write the whole definition again.
+    // FIXME: Make a notification about the specific change (through a listener
+    // interface) so the changes that the serializer records are more
+    // fine grained.
+    data().Definition->setChangedSinceDeserialization(true);
+
     if (CXXConstructorDecl *Constructor = dyn_cast<CXXConstructorDecl>(D)) {
       // If this is the implicit default constructor, note that we have now
       // declared it.