diff --git a/lib/Serialization/ASTReaderDecl.cpp b/lib/Serialization/ASTReaderDecl.cpp
index 97adbf7..e8fe264 100644
--- a/lib/Serialization/ASTReaderDecl.cpp
+++ b/lib/Serialization/ASTReaderDecl.cpp
@@ -833,6 +833,15 @@
     break;
   }
   }
+
+  // Load the key function to avoid deserializing every method so we can
+  // compute it.
+  if (D->IsDefinition) {
+    CXXMethodDecl *Key
+        = cast_or_null<CXXMethodDecl>(Reader.GetDecl(Record[Idx++]));
+    if (Key)
+      C.KeyFunctions[D] = Key;
+  }
 }
 
 void ASTDeclReader::VisitCXXMethodDecl(CXXMethodDecl *D) {
diff --git a/lib/Serialization/ASTWriterDecl.cpp b/lib/Serialization/ASTWriterDecl.cpp
index 3e1ba89..9aaaa48 100644
--- a/lib/Serialization/ASTWriterDecl.cpp
+++ b/lib/Serialization/ASTWriterDecl.cpp
@@ -770,6 +770,11 @@
     Record.push_back(CXXRecNotTemplate);
   }
 
+  // Store the key function to avoid deserializing every method so we can
+  // compute it.
+  if (D->IsDefinition)
+    Writer.AddDeclRef(Context.getKeyFunction(D), Record);
+
   Code = serialization::DECL_CXX_RECORD;
 }