diff --git a/include/clang/Index/USRGeneration.h b/include/clang/Index/USRGeneration.h
index e3a4620..8c661bd 100644
--- a/include/clang/Index/USRGeneration.h
+++ b/include/clang/Index/USRGeneration.h
@@ -31,7 +31,8 @@
 
 /// \brief Generate a USR fragment for an Objective-C class.
 void generateUSRForObjCClass(StringRef Cls, raw_ostream &OS,
-                             StringRef ExtSymbolDefinedIn = "");
+                             StringRef ExtSymbolDefinedIn = "",
+                             StringRef CategoryContextExtSymbolDefinedIn = "");
 
 /// \brief Generate a USR fragment for an Objective-C class category.
 void generateUSRForObjCCategory(StringRef Cls, StringRef Cat, raw_ostream &OS,
@@ -58,6 +59,9 @@
 void generateUSRForGlobalEnum(StringRef EnumName, raw_ostream &OS,
                               StringRef ExtSymbolDefinedIn = "");
 
+/// Generate a USR fragment for an enum constant.
+void generateUSRForEnumConstant(StringRef EnumConstantName, raw_ostream &OS);
+
 /// \brief Generate a USR for a macro, including the USR prefix.
 ///
 /// \returns true on error, false on success.
diff --git a/lib/Index/USRGeneration.cpp b/lib/Index/USRGeneration.cpp
index a83f2fc..af7acaa 100644
--- a/lib/Index/USRGeneration.cpp
+++ b/lib/Index/USRGeneration.cpp
@@ -88,7 +88,8 @@
   void VisitNamespaceAliasDecl(const NamespaceAliasDecl *D);
   void VisitFunctionTemplateDecl(const FunctionTemplateDecl *D);
   void VisitClassTemplateDecl(const ClassTemplateDecl *D);
-  void VisitObjCContainerDecl(const ObjCContainerDecl *CD);
+  void VisitObjCContainerDecl(const ObjCContainerDecl *CD,
+                              const ObjCCategoryDecl *CatD = nullptr);
   void VisitObjCMethodDecl(const ObjCMethodDecl *MD);
   void VisitObjCPropertyDecl(const ObjCPropertyDecl *D);
   void VisitObjCPropertyImplDecl(const ObjCPropertyImplDecl *D);
@@ -138,8 +139,10 @@
   /// itself.
 
   /// Generate a USR for an Objective-C class.
-  void GenObjCClass(StringRef cls, StringRef ext) {
-    generateUSRForObjCClass(cls, Out, ext);
+  void GenObjCClass(StringRef cls, StringRef ExtSymDefinedIn,
+                    StringRef CategoryContextExtSymbolDefinedIn) {
+    generateUSRForObjCClass(cls, Out, ExtSymDefinedIn,
+                            CategoryContextExtSymbolDefinedIn);
   }
 
   /// Generate a USR for an Objective-C class category.
@@ -383,7 +386,16 @@
       IgnoreResults = true;
       return;
     }
-    Visit(ID);
+    auto getCategoryContext = [](const ObjCMethodDecl *D) ->
+                                    const ObjCCategoryDecl * {
+      if (auto *CD = dyn_cast<ObjCCategoryDecl>(D->getDeclContext()))
+        return CD;
+      if (auto *ICD = dyn_cast<ObjCCategoryImplDecl>(D->getDeclContext()))
+        return ICD->getCategoryDecl();
+      return nullptr;
+    };
+    auto *CD = getCategoryContext(D);
+    VisitObjCContainerDecl(ID, CD);
   }
   // Ideally we would use 'GenObjCMethod', but this is such a hot path
   // for Objective-C code that we don't want to use
@@ -392,13 +404,15 @@
       << DeclarationName(D->getSelector());
 }
 
-void USRGenerator::VisitObjCContainerDecl(const ObjCContainerDecl *D) {
+void USRGenerator::VisitObjCContainerDecl(const ObjCContainerDecl *D,
+                                          const ObjCCategoryDecl *CatD) {
   switch (D->getKind()) {
     default:
       llvm_unreachable("Invalid ObjC container.");
     case Decl::ObjCInterface:
     case Decl::ObjCImplementation:
-      GenObjCClass(D->getName(), GetExternalSourceContainer(D));
+      GenObjCClass(D->getName(), GetExternalSourceContainer(D),
+                   GetExternalSourceContainer(CatD));
       break;
     case Decl::ObjCCategory: {
       const ObjCCategoryDecl *CD = cast<ObjCCategoryDecl>(D);
@@ -897,10 +911,26 @@
 // USR generation functions.
 //===----------------------------------------------------------------------===//
 
+static void combineClassAndCategoryExtContainers(StringRef ClsSymDefinedIn,
+                                                 StringRef CatSymDefinedIn,
+                                                 raw_ostream &OS) {
+  if (ClsSymDefinedIn.empty() && CatSymDefinedIn.empty())
+    return;
+  if (CatSymDefinedIn.empty()) {
+    OS << "@M@" << ClsSymDefinedIn << '@';
+    return;
+  }
+  OS << "@CM@" << CatSymDefinedIn << '@';
+  if (ClsSymDefinedIn != CatSymDefinedIn) {
+    OS << ClsSymDefinedIn << '@';
+  }
+}
+
 void clang::index::generateUSRForObjCClass(StringRef Cls, raw_ostream &OS,
-                                           StringRef ExtSymDefinedIn) {
-  if (!ExtSymDefinedIn.empty())
-    OS << "@M@" << ExtSymDefinedIn << '@';
+                                           StringRef ExtSymDefinedIn,
+                                  StringRef CategoryContextExtSymbolDefinedIn) {
+  combineClassAndCategoryExtContainers(ExtSymDefinedIn,
+                                       CategoryContextExtSymbolDefinedIn, OS);
   OS << "objc(cs)" << Cls;
 }
 
@@ -908,16 +938,7 @@
                                               raw_ostream &OS,
                                               StringRef ClsSymDefinedIn,
                                               StringRef CatSymDefinedIn) {
-  if (!CatSymDefinedIn.empty() || !ClsSymDefinedIn.empty()) {
-    OS << "@M@";
-    if (!CatSymDefinedIn.empty() && !ClsSymDefinedIn.empty())
-      OS << CatSymDefinedIn << '-' << ClsSymDefinedIn;
-    else if (!CatSymDefinedIn.empty())
-      OS << CatSymDefinedIn;
-    else
-      OS << ClsSymDefinedIn;
-    OS << '@';
-  }
+  combineClassAndCategoryExtContainers(ClsSymDefinedIn, CatSymDefinedIn, OS);
   OS << "objc(cy)" << Cls << '@' << Cat;
 }
 
@@ -950,6 +971,11 @@
   OS << "@E@" << EnumName;
 }
 
+void clang::index::generateUSRForEnumConstant(StringRef EnumConstantName,
+                                              raw_ostream &OS) {
+  OS << '@' << EnumConstantName;
+}
+
 bool clang::index::generateUSRForDecl(const Decl *D,
                                       SmallVectorImpl<char> &Buf) {
   if (!D)
diff --git a/test/Index/Core/external-source-symbol-attr.m b/test/Index/Core/external-source-symbol-attr.m
index 800a03e..b0e9c15 100644
--- a/test/Index/Core/external-source-symbol-attr.m
+++ b/test/Index/Core/external-source-symbol-attr.m
@@ -2,6 +2,7 @@
 
 #define EXT_DECL(mod_name) __attribute__((external_source_symbol(language="Swift", defined_in=mod_name)))
 #define GEN_DECL(mod_name) __attribute__((external_source_symbol(language="Swift", defined_in=mod_name, generated_declaration)))
+#define PUSH_GEN_DECL(mod_name) push(GEN_DECL(mod_name), apply_to=any(enum, objc_interface, objc_category, objc_protocol))
 
 // This should not be indexed.
 GEN_DECL("some_module")
@@ -37,14 +38,14 @@
 
 EXT_DECL("cat_module")
 @interface I1(cat2)
-// CHECK: [[@LINE-1]]:15 | extension/ObjC | cat2 | c:@M@cat_module-some_module@objc(cy)I1@cat2 |
+// CHECK: [[@LINE-1]]:15 | extension/ObjC | cat2 | c:@CM@cat_module@some_module@objc(cy)I1@cat2 |
 -(void)cat_method2;
-// CHECK: [[@LINE-1]]:8 | instance-method/ObjC | cat_method2 | c:@M@some_module@objc(cs)I1(im)cat_method2
+// CHECK: [[@LINE-1]]:8 | instance-method/ObjC | cat_method2 | c:@CM@cat_module@some_module@objc(cs)I1(im)cat_method2
 @end
 
 #define NS_ENUM(_name, _type) enum _name:_type _name; enum _name : _type
 
-#pragma clang attribute push(GEN_DECL("modname"), apply_to=any(enum, objc_interface, objc_category, objc_protocol))
+#pragma clang attribute PUSH_GEN_DECL("modname")
 
 @interface I3
 // CHECK-NOT: [[@LINE-1]]:12 |
@@ -80,9 +81,20 @@
   [i3 meth];
   // CHECK: [[@LINE-1]]:7 | instance-method/ObjC | meth | c:@M@modname@objc(cs)I3(im)meth |
   [i3 meth2];
-  // CHECK: [[@LINE-1]]:7 | instance-method/ObjC | meth2 | c:@M@modname@objc(cs)I3(im)meth2 |
+  // CHECK: [[@LINE-1]]:7 | instance-method/ObjC | meth2 | c:@CM@modname@objc(cs)I3(im)meth2 |
   [prot2 meth];
   // CHECK: [[@LINE-1]]:10 | instance-method/ObjC | meth | c:@M@modname@objc(pl)ExtProt2(im)meth |
   some = SomeEnumFirst;
   // CHECK: [[@LINE-1]]:10 | enumerator/C | SomeEnumFirst | c:@M@modname@E@SomeEnum@SomeEnumFirst |
 }
+
+#pragma clang attribute PUSH_GEN_DECL("other_mod_for_cat")
+@interface I3(cat_other_mod)
+-(void)meth_other_mod;
+@end
+#pragma clang attribute pop
+
+void test3(I3 *i3) {
+  [i3 meth_other_mod];
+  // CHECK: [[@LINE-1]]:7 | instance-method/ObjC | meth_other_mod | c:@CM@other_mod_for_cat@modname@objc(cs)I3(im)meth_other_mod |
+}