diff --git a/clang-tools-extra/clangd/ClangdLSPServer.cpp b/clang-tools-extra/clangd/ClangdLSPServer.cpp
--- a/clang-tools-extra/clangd/ClangdLSPServer.cpp
+++ b/clang-tools-extra/clangd/ClangdLSPServer.cpp
@@ -1007,6 +1007,20 @@
         for (const auto &T : *Tweaks)
           Actions.push_back(toCodeAction(T, File, Selection));
 
+        // If there's exactly one quick-fix, call it "preferred".
+        // We never consider refactorings etc as preferred.
+        CodeAction *OnlyFix = nullptr;
+        for (auto &Action : Actions) {
+          if (Action.kind && *Action.kind == CodeAction::QUICKFIX_KIND) {
+            if (OnlyFix) {
+              OnlyFix->isPreferred = false;
+              break;
+            }
+            Action.isPreferred = true;
+            OnlyFix = &Action;
+          }
+        }
+
         if (SupportsCodeAction)
           return Reply(llvm::json::Array(Actions));
         std::vector<Command> Commands;
diff --git a/clang-tools-extra/clangd/Diagnostics.cpp b/clang-tools-extra/clangd/Diagnostics.cpp
--- a/clang-tools-extra/clangd/Diagnostics.cpp
+++ b/clang-tools-extra/clangd/Diagnostics.cpp
@@ -411,6 +411,8 @@
     Main.codeActions.emplace();
     for (const auto &Fix : D.Fixes)
       Main.codeActions->push_back(toCodeAction(Fix, File));
+    if (Main.codeActions->size() == 1)
+      Main.codeActions->front().isPreferred = true;
   }
   if (Opts.SendDiagnosticCategory && !D.Category.empty())
     Main.category = D.Category;
diff --git a/clang-tools-extra/clangd/Protocol.h b/clang-tools-extra/clangd/Protocol.h
--- a/clang-tools-extra/clangd/Protocol.h
+++ b/clang-tools-extra/clangd/Protocol.h
@@ -952,6 +952,13 @@
   /// The diagnostics that this code action resolves.
   llvm::Optional<std::vector<Diagnostic>> diagnostics;
 
+  /// Marks this as a preferred action. Preferred actions are used by the
+  /// `auto fix` command and can be targeted by keybindings.
+  /// A quick fix should be marked preferred if it properly addresses the
+  /// underlying error. A refactoring should be marked preferred if it is the
+  /// most reasonable choice of actions to take.
+  bool isPreferred = false;
+
   /// The workspace edit this code action performs.
   llvm::Optional<WorkspaceEdit> edit;
 
diff --git a/clang-tools-extra/clangd/Protocol.cpp b/clang-tools-extra/clangd/Protocol.cpp
--- a/clang-tools-extra/clangd/Protocol.cpp
+++ b/clang-tools-extra/clangd/Protocol.cpp
@@ -740,6 +740,8 @@
     CodeAction["kind"] = *CA.kind;
   if (CA.diagnostics)
     CodeAction["diagnostics"] = llvm::json::Array(*CA.diagnostics);
+  if (CA.isPreferred)
+    CodeAction["isPreferred"] = true;
   if (CA.edit)
     CodeAction["edit"] = *CA.edit;
   if (CA.command)
diff --git a/clang-tools-extra/clangd/test/fixits-embed-in-diagnostic.test b/clang-tools-extra/clangd/test/fixits-embed-in-diagnostic.test
--- a/clang-tools-extra/clangd/test/fixits-embed-in-diagnostic.test
+++ b/clang-tools-extra/clangd/test/fixits-embed-in-diagnostic.test
@@ -28,6 +28,7 @@
 # CHECK-NEXT:                ]
 # CHECK-NEXT:              }
 # CHECK-NEXT:            },
+# CHECK-NEXT:            "isPreferred": true,
 # CHECK-NEXT:            "kind": "quickfix",
 # CHECK-NEXT:            "title": "change 'union' to 'struct'"
 # CHECK-NEXT:          }