Index: clang/include/clang/AST/DeclObjC.h
===================================================================
--- clang/include/clang/AST/DeclObjC.h
+++ clang/include/clang/AST/DeclObjC.h
@@ -1226,7 +1226,8 @@
   /// which will be NULL if this class has not yet been defined.
   ///
   /// The bit indicates when we don't need to check for out-of-date
-  /// declarations. It will be set unless modules are enabled.
+  /// declarations. It will be set unless there is an ExternalASTSource that
+  /// could provide a definition.
   llvm::PointerIntPair<DefinitionData *, 1, bool> Data;
 
   ObjCInterfaceDecl(const ASTContext &C, DeclContext *DC, SourceLocation AtLoc,
@@ -1515,7 +1516,7 @@
     // If the name of this class is out-of-date, bring it up-to-date, which
     // might bring in a definition.
     // Note: a null value indicates that we don't have a definition and that
-    // modules are enabled.
+    // there is a ExternalASTSource that could provide a definition.
     if (!Data.getOpaqueValue())
       getMostRecentDecl();
 
@@ -2061,7 +2062,8 @@
   /// which will be NULL if this class has not yet been defined.
   ///
   /// The bit indicates when we don't need to check for out-of-date
-  /// declarations. It will be set unless modules are enabled.
+  /// declarations. It will be set unless there is an ExternalASTSource that
+  /// could provide a definition.
   llvm::PointerIntPair<DefinitionData *, 1, bool> Data;
 
   ObjCProtocolDecl(ASTContext &C, DeclContext *DC, IdentifierInfo *Id,
@@ -2193,7 +2195,7 @@
     // If the name of this protocol is out-of-date, bring it up-to-date, which
     // might bring in a definition.
     // Note: a null value indicates that we don't have a definition and that
-    // modules are enabled.
+    // there is a ExternalASTSource that could provide a definition.
     if (!Data.getOpaqueValue())
       getMostRecentDecl();
 
Index: clang/lib/AST/DeclObjC.cpp
===================================================================
--- clang/lib/AST/DeclObjC.cpp
+++ clang/lib/AST/DeclObjC.cpp
@@ -1507,7 +1507,7 @@
   auto *Result = new (C, DC)
       ObjCInterfaceDecl(C, DC, atLoc, Id, typeParamList, ClassLoc, PrevDecl,
                         isInternal);
-  Result->Data.setInt(!C.getLangOpts().Modules);
+  Result->Data.setInt(!C.getExternalSource());
   C.getObjCInterfaceType(Result, PrevDecl);
   return Result;
 }
@@ -1517,7 +1517,7 @@
   auto *Result = new (C, ID)
       ObjCInterfaceDecl(C, nullptr, SourceLocation(), nullptr, nullptr,
                         SourceLocation(), nullptr, false);
-  Result->Data.setInt(!C.getLangOpts().Modules);
+  Result->Data.setInt(!C.getExternalSource());
   return Result;
 }
 
@@ -1903,7 +1903,7 @@
                                            ObjCProtocolDecl *PrevDecl) {
   auto *Result =
       new (C, DC) ObjCProtocolDecl(C, DC, Id, nameLoc, atStartLoc, PrevDecl);
-  Result->Data.setInt(!C.getLangOpts().Modules);
+  Result->Data.setInt(!C.getExternalSource());
   return Result;
 }
 
@@ -1912,7 +1912,7 @@
   ObjCProtocolDecl *Result =
       new (C, ID) ObjCProtocolDecl(C, nullptr, nullptr, SourceLocation(),
                                    SourceLocation(), nullptr);
-  Result->Data.setInt(!C.getLangOpts().Modules);
+  Result->Data.setInt(!C.getExternalSource());
   return Result;
 }