Index: clang/lib/Sema/SemaTemplateInstantiate.cpp
===================================================================
--- clang/lib/Sema/SemaTemplateInstantiate.cpp
+++ clang/lib/Sema/SemaTemplateInstantiate.cpp
@@ -3624,11 +3624,13 @@
   llvm::PointerUnion<Decl *, DeclArgumentPack *> &Stored = LocalDecls[D];
   if (Stored.isNull()) {
 #ifndef NDEBUG
-    // It should not be present in any surrounding scope either.
+    // It should not be present in any surrounding scope either except for
+    // recursive lambda functions.
     LocalInstantiationScope *Current = this;
     while (Current->CombineWithOuterScope && Current->Outer) {
       Current = Current->Outer;
-      assert(Current->LocalDecls.find(D) == Current->LocalDecls.end() &&
+      assert((isLambdaCallOperator(D->getDeclContext()) ||
+              Current->LocalDecls.find(D) == Current->LocalDecls.end()) &&
              "Instantiated local in inner and outer scopes");
     }
 #endif
@@ -3649,10 +3651,12 @@
 
 void LocalInstantiationScope::MakeInstantiatedLocalArgPack(const Decl *D) {
 #ifndef NDEBUG
-  // This should be the first time we've been told about this decl.
+  // This should be the first time we've been told about this decl except for
+  // recursive lambda functions.
   for (LocalInstantiationScope *Current = this;
        Current && Current->CombineWithOuterScope; Current = Current->Outer)
-    assert(Current->LocalDecls.find(D) == Current->LocalDecls.end() &&
+    assert((isLambdaCallOperator(D->getDeclContext()) ||
+            Current->LocalDecls.find(D) == Current->LocalDecls.end()) &&
            "Creating local pack after instantiation of local");
 #endif
 
Index: clang/test/SemaCXX/recursive-lambda.cpp
===================================================================
--- /dev/null
+++ clang/test/SemaCXX/recursive-lambda.cpp
@@ -0,0 +1,34 @@
+// RUN: %clang_cc1 -std=c++17 -fsyntax-only -verify %s
+
+// expected-no-diagnostics
+
+// Check recursive instantiation of lambda does not cause assertion.
+// lambda function `f` in `fun1` is instantiated twice: first
+// as f(f, Number<1>), then as f(f, Number<0>). The
+// LocalInstantiationScopes of these two instantiations both contain
+// `f` and `i`. Clang should not assert for that.
+
+template <unsigned v>
+struct Number
+{
+   static constexpr unsigned value = v;
+};
+
+template <unsigned IBegin = 0,
+          unsigned IEnd = 1>
+constexpr auto fun1(Number<IBegin> = Number<0>{}, Number<IEnd>  = Number<1>{})
+{
+  auto f = [&](auto fs, auto i) {
+    if constexpr(i.value > 0)
+    {
+      return fs(fs, Number<IBegin>{});
+    }
+  };
+
+  return f(f, Number<IEnd>{});
+}
+
+
+void fun2() {
+  fun1();
+}