diff --git a/lib/Serialization/ASTReader.cpp b/lib/Serialization/ASTReader.cpp
index f09873a..6497b78 100644
--- a/lib/Serialization/ASTReader.cpp
+++ b/lib/Serialization/ASTReader.cpp
@@ -3284,6 +3284,9 @@
 /// source each time it is called, and is meant to be used via a
 /// LazyOffsetPtr (which is used by Decls for the body of functions, etc).
 Stmt *ASTReader::GetExternalDeclStmt(uint64_t Offset) {
+  // Switch case IDs are per Decl.
+  ClearSwitchCaseIDs();
+
   // Offset here is a global offset across the entire chain.
   for (unsigned I = 0, N = Chain.size(); I != N; ++I) {
     PerFileData &F = *Chain[N - I - 1];
@@ -4252,6 +4255,10 @@
   return SwitchCaseStmts[ID];
 }
 
+void ASTReader::ClearSwitchCaseIDs() {
+  SwitchCaseStmts.clear();
+}
+
 /// \brief Record that the given label statement has been
 /// deserialized and has the given ID.
 void ASTReader::RecordLabelStmt(LabelStmt *S, unsigned ID) {
diff --git a/lib/Serialization/ASTWriterDecl.cpp b/lib/Serialization/ASTWriterDecl.cpp
index 3c6dd9b..37c7765 100644
--- a/lib/Serialization/ASTWriterDecl.cpp
+++ b/lib/Serialization/ASTWriterDecl.cpp
@@ -1128,6 +1128,9 @@
 }
 
 void ASTWriter::WriteDecl(ASTContext &Context, Decl *D) {
+  // Switch case IDs are per Decl.
+  ClearSwitchCaseIDs();
+
   RecordData Record;
   ASTDeclWriter W(*this, Context, Record);
 
diff --git a/lib/Serialization/ASTWriterStmt.cpp b/lib/Serialization/ASTWriterStmt.cpp
index 33b70e9..fc8e9e0 100644
--- a/lib/Serialization/ASTWriterStmt.cpp
+++ b/lib/Serialization/ASTWriterStmt.cpp
@@ -1311,6 +1311,10 @@
   return SwitchCaseIDs[S];
 }
 
+void ASTWriter::ClearSwitchCaseIDs() {
+  SwitchCaseIDs.clear();
+}
+
 /// \brief Retrieve the ID for the given label statement, which may
 /// or may not have been emitted yet.
 unsigned ASTWriter::GetLabelID(LabelStmt *S) {