diff --git a/clang/include/clang/Basic/DiagnosticSemaKinds.td b/clang/include/clang/Basic/DiagnosticSemaKinds.td
--- a/clang/include/clang/Basic/DiagnosticSemaKinds.td
+++ b/clang/include/clang/Basic/DiagnosticSemaKinds.td
@@ -7896,6 +7896,9 @@
   def warn_cxx17_compat_lambda_def_ctor_assign : Warning<
     "%select{default construction|assignment}0 of lambda is incompatible with "
     "C++ standards before C++20">, InGroup<CXXPre20Compat>, DefaultIgnore;
+
+  def err_local_variable_as_default_in_template : Error<
+  "local variable '%0' may not be used as default parameter">;
 }
 
 def err_return_in_captured_stmt : Error<
diff --git a/clang/lib/Sema/SemaTemplate.cpp b/clang/lib/Sema/SemaTemplate.cpp
--- a/clang/lib/Sema/SemaTemplate.cpp
+++ b/clang/lib/Sema/SemaTemplate.cpp
@@ -1587,6 +1587,15 @@
 
   // Check the well-formedness of the default template argument, if provided.
   if (Default) {
+    // Local variables may not be used as default template arguments.
+    if (auto *DRE = dyn_cast<DeclRefExpr>(Default)) {
+      if (VarDecl *VD = dyn_cast<VarDecl>(DRE->getDecl())) {
+        if(VD->hasLocalStorage()) {
+          Diag(DRE->getLocation(), diag::err_local_variable_as_default_in_template) << VD->getNameAsString();
+        }
+      }
+    }
+
     // Check for unexpanded parameter packs.
     if (DiagnoseUnexpandedParameterPack(Default, UPPC_DefaultArgument))
       return Param;
diff --git a/clang/test/SemaTemplate/default-template-arguments.cpp b/clang/test/SemaTemplate/default-template-arguments.cpp
new file mode 100644
--- /dev/null
+++ b/clang/test/SemaTemplate/default-template-arguments.cpp
@@ -0,0 +1,14 @@
+// RUN: %clang_cc1 -fsyntax-only -std=c++20 -verify %s
+
+namespace GH48755 {
+constexpr auto z = 2;
+
+auto f() {
+  const auto x = 1;
+
+  auto lambda1 = [] <auto y = x> {}; // expected-error {{local variables may not be used as default parameters}}
+  auto lambda2 = [] <auto y = 42> {};
+  auto lambda3 = [] <auto y = z> {};
+  auto lambda4 = [] <auto y> {};
+}
+}