diff --git a/clang/lib/Sema/SemaExpr.cpp b/clang/lib/Sema/SemaExpr.cpp
--- a/clang/lib/Sema/SemaExpr.cpp
+++ b/clang/lib/Sema/SemaExpr.cpp
@@ -19082,6 +19082,14 @@
     }
   }
 
+  // If the variable is used in a default argument expression of a lambda call
+  // operator, switch to the enclosing context to sync up with the function
+  // scope.
+  if (isLambdaCallOperator(DC))
+    if (auto *PVD = dyn_cast_or_null<ParmVarDecl>(
+            ExprEvalContexts.back().ManglingContextDecl))
+      if (PVD->getDeclContext() == DC)
+        DC = getLambdaAwareParentOfDeclContext(DC);
 
   // If the variable is declared in the current context, there is no need to
   // capture it.
diff --git a/clang/test/SemaCXX/lambda-default-arg.cpp b/clang/test/SemaCXX/lambda-default-arg.cpp
new file mode 100644
--- /dev/null
+++ b/clang/test/SemaCXX/lambda-default-arg.cpp
@@ -0,0 +1,27 @@
+// RUN: %clang_cc1 -std=c++17 -verify -fsyntax-only %s
+
+template <class T> bool test0() {
+  constexpr float a = 1e-5f;
+  return [=](float b = a) -> bool {
+    return a < 0;
+  }();
+}
+
+bool b0 = test0<int>();
+
+template <class T> bool test1() {
+  float a = 1e-5f;
+  return [=](float b = a) -> bool { // expected-error {{default argument references local variable 'a'}}
+    return a < 0;
+  }();
+}
+
+bool b1 = test1<int>();
+
+template <class T> bool test2(float a = 1e-5f) {
+  return [=](int b = sizeof(a)) -> bool {
+    return b;
+  }();
+}
+
+bool b2 = test2<int>();