diff --git a/clang/lib/Serialization/ASTReader.cpp b/clang/lib/Serialization/ASTReader.cpp
--- a/clang/lib/Serialization/ASTReader.cpp
+++ b/clang/lib/Serialization/ASTReader.cpp
@@ -7461,8 +7461,6 @@
 /// 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.
   RecordLocation Loc = getLocalBitOffset(Offset);
@@ -9067,8 +9065,7 @@
 /// Record that the given ID maps to the given switch-case
 /// statement.
 void ASTReader::RecordSwitchCaseID(SwitchCase *SC, unsigned ID) {
-  assert((*CurrSwitchCaseStmts)[ID] == nullptr &&
-         "Already have a SwitchCase with this ID");
+  // We may already have a SwitchCase with this ID, drop the existing.
   (*CurrSwitchCaseStmts)[ID] = SC;
 }
 
diff --git a/clang/lib/Serialization/ASTWriterDecl.cpp b/clang/lib/Serialization/ASTWriterDecl.cpp
--- a/clang/lib/Serialization/ASTWriterDecl.cpp
+++ b/clang/lib/Serialization/ASTWriterDecl.cpp
@@ -2453,9 +2453,6 @@
 }
 
 void ASTRecordWriter::AddFunctionDefinition(const FunctionDecl *FD) {
-  // Switch case IDs are per function body.
-  Writer->ClearSwitchCaseIDs();
-
   assert(FD->doesThisDeclarationHaveABody());
   bool ModulesCodegen = false;
   if (Writer->WritingModule && !FD->isDependentContext()) {
diff --git a/clang/lib/Serialization/ASTWriterStmt.cpp b/clang/lib/Serialization/ASTWriterStmt.cpp
--- a/clang/lib/Serialization/ASTWriterStmt.cpp
+++ b/clang/lib/Serialization/ASTWriterStmt.cpp
@@ -2611,11 +2611,12 @@
 //===----------------------------------------------------------------------===//
 
 unsigned ASTWriter::RecordSwitchCaseID(SwitchCase *S) {
-  assert(SwitchCaseIDs.find(S) == SwitchCaseIDs.end() &&
-         "SwitchCase recorded twice");
   unsigned NextID = SwitchCaseIDs.size();
-  SwitchCaseIDs[S] = NextID;
-  return NextID;
+  assert(NextID < UINT_MAX && "Too many SwitchCase to serialize");
+  // If we already recorded this SwitchCase then just return with its ID, else
+  // insert it with the next ID.
+  auto Res = SwitchCaseIDs.insert({S, NextID});
+  return Res.first->second;
 }
 
 unsigned ASTWriter::getSwitchCaseID(SwitchCase *S) {
diff --git a/clang/test/AST/ast-dump-lambda.cpp b/clang/test/AST/ast-dump-lambda.cpp
--- a/clang/test/AST/ast-dump-lambda.cpp
+++ b/clang/test/AST/ast-dump-lambda.cpp
@@ -34,6 +34,21 @@
   []() noexcept {};
   []() -> int { return 0; };
 }
+
+class {
+public:
+  enum {} a;
+} b;
+void should_not_crash_with_switch_in_lambda() {
+  switch (b.a)
+  default:;
+    enum { e } d;
+  auto f = [d] {
+    switch (d)
+    case e:;
+  };
+}
+
 // CHECK:Dumping test:
 // CHECK-NEXT:FunctionTemplateDecl {{.*}} <{{.*}}ast-dump-lambda.cpp:15:1, line:36:1> line:15:32{{( imported)?}} test
 // CHECK-NEXT:|-TemplateTypeParmDecl {{.*}} <col:11, col:23> col:23{{( imported)?}} referenced typename depth 0 index 0 ... Ts