Index: lib/AST/Comment.cpp
===================================================================
--- lib/AST/Comment.cpp
+++ lib/AST/Comment.cpp
@@ -226,12 +226,15 @@
   case Decl::Namespace:
     Kind = NamespaceKind;
     break;
+  case Decl::TypeAlias:
   case Decl::Typedef: {
     Kind = TypedefKind;
-    // If this is a typedef to something we consider a function, extract
+    // If this is a typedef / using to something we consider a function, extract
     // arguments and return type.
-    const TypedefDecl *TD = cast<TypedefDecl>(CommentDecl);
-    const TypeSourceInfo *TSI = TD->getTypeSourceInfo();
+    const TypeSourceInfo *TSI =
+        K == Decl::Typedef
+            ? cast<TypedefDecl>(CommentDecl)->getTypeSourceInfo()
+            : cast<TypeAliasDecl>(CommentDecl)->getTypeSourceInfo();
     if (!TSI)
       break;
     TypeLoc TL = TSI->getTypeLoc().getUnqualifiedLoc();
@@ -302,9 +305,6 @@
     }
     break;
   }
-  case Decl::TypeAlias:
-    Kind = TypedefKind;
-    break;
   case Decl::TypeAliasTemplate: {
     const TypeAliasTemplateDecl *TAT = cast<TypeAliasTemplateDecl>(CommentDecl);
     Kind = TypedefKind;
Index: test/Sema/warn-documentation.cpp
===================================================================
--- test/Sema/warn-documentation.cpp
+++ test/Sema/warn-documentation.cpp
@@ -368,6 +368,69 @@
 /// \param aaa Meow.
 typedef foo::not_a_function_wrapper<1> test_not_function_like_typedef4;
 
+// expected-warning@+2 {{parameter 'bbb' not found in the function declaration}} expected-note@+2 {{did you mean 'ccc'?}}
+/// \param aaa Meow.
+/// \param bbb Bbb.
+/// \returns aaa.
+using test_function_like_using1 = int (int aaa, int ccc);
+
+// expected-warning@+2 {{parameter 'bbb' not found in the function declaration}} expected-note@+2 {{did you mean 'ccc'?}}
+/// \param aaa Meow.
+/// \param bbb Bbb.
+/// \returns aaa.
+using test_function_like_using2 = int (*)(int aaa, int ccc);
+
+// expected-warning@+2 {{parameter 'bbb' not found in the function declaration}} expected-note@+2 {{did you mean 'ccc'?}}
+/// \param aaa Meow.
+/// \param bbb Bbb.
+/// \returns aaa.
+using test_function_like_using3 = int (* const)(int aaa, int ccc);
+
+// expected-warning@+2 {{parameter 'bbb' not found in the function declaration}} expected-note@+2 {{did you mean 'ccc'?}}
+/// \param aaa Meow.
+/// \param bbb Bbb.
+/// \returns aaa.
+using test_function_like_using4 = int (C::*)(int aaa, int ccc);
+
+// expected-warning@+2 {{parameter 'bbb' not found in the function declaration}} expected-note@+2 {{did you mean 'ccc'?}}
+/// \param aaa Meow.
+/// \param bbb Bbb.
+/// \returns aaa.
+using test_function_like_using5 = foo::function_wrapper<int (int aaa, int ccc)>;
+
+// expected-warning@+2 {{parameter 'bbb' not found in the function declaration}} expected-note@+2 {{did you mean 'ccc'?}}
+/// \param aaa Meow.
+/// \param bbb Bbb.
+/// \returns aaa.
+using test_function_like_using6 = foo::function_wrapper<int (int aaa, int ccc)> *;
+
+// expected-warning@+2 {{parameter 'bbb' not found in the function declaration}} expected-note@+2 {{did you mean 'ccc'?}}
+/// \param aaa Meow.
+/// \param bbb Bbb.
+/// \returns aaa.
+using test_function_like_using7 = foo::function_wrapper<int (int aaa, int ccc)> &;
+
+// expected-warning@+2 {{parameter 'bbb' not found in the function declaration}} expected-note@+2 {{did you mean 'ccc'?}}
+/// \param aaa Meow.
+/// \param bbb Bbb.
+/// \returns aaa.
+using test_function_like_using8 = foo::function_wrapper<int (int aaa, int ccc)> &&;
+
+using test_not_function_like_using1 = int (*)(int aaa);
+
+// expected-warning@+1 {{'\param' command used in a comment that is not attached to a function declaration}}
+/// \param aaa Meow.
+using test_not_function_like_using2 = test_not_function_like_using1;
+
+// Check that the diagnostic uses the same command marker as the comment.
+// expected-warning@+1 {{'@param' command used in a comment that is not attached to a function declaration}}
+/// @param aaa Meow.
+using test_not_function_like_using3 = unsigned int;
+
+// expected-warning@+1 {{'\param' command used in a comment that is not attached to a function declaration}}
+/// \param aaa Meow.
+using test_not_function_like_using4 = foo::not_a_function_wrapper<1>;
+
 /// \param aaa Aaa
 /// \param ... Vararg
 int test_vararg_param1(int aaa, ...);