Index: include/clang/Sema/Sema.h
===================================================================
--- include/clang/Sema/Sema.h
+++ include/clang/Sema/Sema.h
@@ -7318,6 +7318,12 @@
                                ArrayRef<IdentifierLocPair> ProtocolId,
                                SmallVectorImpl<Decl *> &Protocols);
 
+  void DiagnoseTypeArgsAndProtocols(IdentifierInfo *ProtocolId,
+                                    SourceLocation ProtocolLoc,
+                                    IdentifierInfo *TypeArgId,
+                                    SourceLocation TypeArgLoc,
+                                    bool SelectProtocolFirst = false);
+
   /// Given a list of identifiers (and their locations), resolve the
   /// names to either Objective-C protocol qualifiers or type
   /// arguments, as appropriate.
Index: lib/Parse/ParseObjc.cpp
===================================================================
--- lib/Parse/ParseObjc.cpp
+++ lib/Parse/ParseObjc.cpp
@@ -1694,10 +1694,15 @@
   }
 
   // We syntactically matched a type argument, so commit to parsing
-  // type arguments.
+  // type arguments. Finding protocol arguments after here is an error.
 
   // Convert the identifiers into type arguments.
   bool invalid = false;
+  IdentifierInfo *foundProtocolId = nullptr;
+  SourceLocation foundProtocolSrcLoc;
+  SmallVector<IdentifierInfo *, 2> unknownTypeArgs;
+  SmallVector<SourceLocation, 2> unknownTypeArgsLoc;
+
   for (unsigned i = 0, n = identifiers.size(); i != n; ++i) {
     ParsedType typeArg
       = Actions.getTypeName(*identifiers[i], identifierLocs[i], getCurScope());
@@ -1717,11 +1722,24 @@
         invalid = true;
     } else {
       invalid = true;
+      auto *P = Actions.LookupProtocol(identifiers[i], identifierLocs[i]);
+      if (!P) {
+        unknownTypeArgs.push_back(identifiers[i]);
+        unknownTypeArgsLoc.push_back(identifierLocs[i]);
+        continue;
+      }
+      if (!foundProtocolId) {
+        foundProtocolId = identifiers[i];
+        foundProtocolSrcLoc = identifierLocs[i];
+      }
     }
   }
 
   // Continue parsing type-names.
+  IdentifierInfo *foundValidTypeId = nullptr;
+  SourceLocation foundValidTypeSrcLoc;
   do {
+    Token CurTypeTok = Tok;
     TypeResult typeArg = ParseTypeName();
 
     // Consume the '...' for a pack expansion.
@@ -1733,11 +1751,28 @@
 
     if (typeArg.isUsable()) {
       typeArgs.push_back(typeArg.get());
+      if (!foundValidTypeId) {
+        foundValidTypeId = CurTypeTok.getIdentifierInfo();
+        foundValidTypeSrcLoc = CurTypeTok.getLocation();
+      }
     } else {
       invalid = true;
     }
   } while (TryConsumeToken(tok::comma));
 
+  // Diagnose the mix between type args and protocols.
+  if (foundProtocolId && foundValidTypeId)
+    Actions.DiagnoseTypeArgsAndProtocols(foundProtocolId, foundProtocolSrcLoc,
+                                         foundValidTypeId,
+                                         foundValidTypeSrcLoc);
+
+  // Diagnose unknown arg types.
+  ParsedType T;
+  if (unknownTypeArgs.size())
+    for (unsigned i = 0, e = unknownTypeArgsLoc.size(); i < e; ++i)
+      Actions.DiagnoseUnknownTypeName(unknownTypeArgs[i], unknownTypeArgsLoc[i],
+                                      getCurScope(), nullptr, T);
+
   // Parse the closing '>'.
   SourceLocation rAngleLoc;
   (void)ParseGreaterThanInTemplateList(rAngleLoc, consumeLastToken,
Index: lib/Sema/SemaDeclObjC.cpp
===================================================================
--- lib/Sema/SemaDeclObjC.cpp
+++ lib/Sema/SemaDeclObjC.cpp
@@ -1303,6 +1303,16 @@
 };
 } // end anonymous namespace
 
+void Sema::DiagnoseTypeArgsAndProtocols(IdentifierInfo *ProtocolId,
+                                        SourceLocation ProtocolLoc,
+                                        IdentifierInfo *TypeArgId,
+                                        SourceLocation TypeArgLoc,
+                                        bool SelectProtocolFirst) {
+  Diag(TypeArgLoc, diag::err_objc_type_args_and_protocols)
+      << SelectProtocolFirst << TypeArgId << ProtocolId
+      << SourceRange(ProtocolLoc);
+}
+
 void Sema::actOnObjCTypeArgsOrProtocolQualifiers(
        Scope *S,
        ParsedType baseType,
@@ -1570,11 +1580,9 @@
 
       // We have a conflict: some names refer to protocols and others
       // refer to types.
-      Diag(identifierLocs[i], diag::err_objc_type_args_and_protocols)
-        << (protocols[i] != nullptr)
-        << identifiers[i]
-        << identifiers[0]
-        << SourceRange(identifierLocs[0]);
+      DiagnoseTypeArgsAndProtocols(identifiers[0], identifierLocs[0],
+                                   identifiers[i], identifierLocs[i],
+                                   protocols[i] != nullptr);
 
       protocols.clear();
       typeArgs.clear();
Index: test/SemaObjC/parameterized_classes.m
===================================================================
--- test/SemaObjC/parameterized_classes.m
+++ test/SemaObjC/parameterized_classes.m
@@ -240,6 +240,9 @@
 
 // Type/protocol conflict.
 typedef PC4<NSCopying, ObjCStringRef> typeArgsProtocolQualsConflict1; // expected-error{{angle brackets contain both a type ('ObjCStringRef') and a protocol ('NSCopying')}}
+typedef PC4<NSCopying, NSString *> typeArgsProtocolQualsConflict2; // expected-error{{angle brackets contain both a type ('NSString') and a protocol ('NSCopying')}}
+typedef PC4<NSCopying, UnknownType, NSString *> typeArgsProtocolQualsConflict3; // expected-error{{angle brackets contain both a type ('NSString') and a protocol ('NSCopying')}} expected-error{{unknown type name 'UnknownType'}}
+typedef PC4<UnknownType, NSString *> typeArgsProtocolQualsConflict4; // expected-error{{unknown type name 'UnknownType'}}
 
 // Handling the '>>' in type argument lists.
 typedef PC4<id<NSCopying>, NSObject *, id<NSObject>> typeArgs6;