diff --git a/clang-tools-extra/clangd/refactor/tweaks/DefineOutline.cpp b/clang-tools-extra/clangd/refactor/tweaks/DefineOutline.cpp
--- a/clang-tools-extra/clangd/refactor/tweaks/DefineOutline.cpp
+++ b/clang-tools-extra/clangd/refactor/tweaks/DefineOutline.cpp
@@ -397,6 +397,14 @@
     if (auto *MD = llvm::dyn_cast<CXXMethodDecl>(Source)) {
       if (MD->getParent()->isTemplated())
         return false;
+
+      // The refactoring is meaningless for unnamed classes.
+      const auto *Parent = MD->getParent();
+      while (Parent) {
+        if (Parent->getName().empty())
+          return false;
+        Parent = llvm::dyn_cast_or_null<CXXRecordDecl>(Parent->getParent());
+      }
     }
 
     // Note that we don't check whether an implementation file exists or not in
diff --git a/clang-tools-extra/clangd/unittests/tweaks/DefineOutlineTests.cpp b/clang-tools-extra/clangd/unittests/tweaks/DefineOutlineTests.cpp
--- a/clang-tools-extra/clangd/unittests/tweaks/DefineOutlineTests.cpp
+++ b/clang-tools-extra/clangd/unittests/tweaks/DefineOutlineTests.cpp
@@ -84,6 +84,23 @@
     template <typename> void fo^o() {};
     template <> void fo^o<int>() {};
   )cpp");
+
+  // Not available on methods of unnamed classes.
+  EXPECT_UNAVAILABLE(R"cpp(
+    struct Foo {
+      struct { void b^ar() {} } Bar;
+    };
+  )cpp");
+
+  // Not available on methods of named classes with unnamed parent in parents
+  // nesting.
+  EXPECT_UNAVAILABLE(R"cpp(
+    struct Foo {
+      struct {
+        struct Bar { void b^ar() {} };
+      } Baz;
+    };
+  )cpp");
 }
 
 TEST_F(DefineOutlineTest, FailsWithoutSource) {