diff --git a/components/ideintf/unitresources.pas b/components/ideintf/unitresources.pas
index 5440fb3e5c..2b7c6c6721 100644
--- a/components/ideintf/unitresources.pas
+++ b/components/ideintf/unitresources.pas
@@ -23,7 +23,7 @@ uses
   // LCL
   LCLMemManager, Forms, LResources,
   // LazUtils
-  UITypes;
+  UITypes, LazStringUtils;
 
 type
 
@@ -45,7 +45,7 @@ type
       out MissingClasses: TStrings// e.g. MyFrame2:TMyFrame
       ): TModalResult; virtual; abstract;
     class function Priority: integer; virtual; // higher priority is tested first
-    class function DefaultComponentClass: TComponentClass; virtual;
+    class function DefaultComponentClass(aClassName: string): TComponentClass; virtual;
     class function FindComponentClass({%H-}aClassName: string): TComponentClass; virtual;
   end;
   TUnitResourcefileFormatClass = class of TUnitResourcefileFormat;
@@ -62,7 +62,7 @@ type
     class function GetClassNameFromStream(s: TStream; out IsInherited: Boolean): shortstring; override;
     class function CreateReader(s: TStream; var DestroyDriver: boolean): TReader; override;
     class function CreateWriter(s: TStream; var DestroyDriver: boolean): TWriter; override;
-    class function DefaultComponentClass: TComponentClass; override;
+    class function DefaultComponentClass(aClassName: string): TComponentClass; override;
     class function FindComponentClass(aClassName: string): TComponentClass; override;
   end;
 
@@ -150,9 +150,15 @@ begin
   Result := CreateLRSWriter(s, DestroyDriver);
 end;
 
-class function TCustomLFMUnitResourceFileFormat.DefaultComponentClass: TComponentClass;
-begin
-  Result := FormEditingHook.StandardDesignerBaseClasses[DesignerBaseClassId_TForm];
+class function TCustomLFMUnitResourceFileFormat.DefaultComponentClass(
+  aClassName: string): TComponentClass;
+begin   // Use heuristics to get a default class.
+  if PosI('DataModule',aClassName) > 0 then
+    Result:=FormEditingHook.StandardDesignerBaseClasses[DesignerBaseClassId_TDataModule]
+  else if PosI('Frame',aClassName) > 0 then
+    Result:=FormEditingHook.StandardDesignerBaseClasses[DesignerBaseClassId_TFrame]
+  else
+    Result := FormEditingHook.StandardDesignerBaseClasses[DesignerBaseClassId_TForm];
 end;
 
 class function TCustomLFMUnitResourceFileFormat.FindComponentClass(
@@ -175,7 +181,7 @@ begin
   Result:=0;
 end;
 
-class function TUnitResourcefileFormat.DefaultComponentClass: TComponentClass;
+class function TUnitResourcefileFormat.DefaultComponentClass(aClassName: string): TComponentClass;
 begin
   Result:=TForm;
 end;
diff --git a/ide/sourcefilemanager.pas b/ide/sourcefilemanager.pas
index f1a61c103d..fe1dbc123c 100644
--- a/ide/sourcefilemanager.pas
+++ b/ide/sourcefilemanager.pas
@@ -56,7 +56,7 @@ uses
   SourceSynEditor, SourceEditor, EditorOptions, EnvironmentOpts, CustomFormEditor,
   ControlSelection, FormEditor, EmptyMethodsDlg, BaseDebugManager, TransferMacros,
   BuildManager, EditorMacroListViewer, FindRenameIdentifier, BuildModesManager,
-  ViewUnit_Dlg, InputHistory, CheckLFMDlg, etMessagesWnd,
+  ViewUnit_Dlg, InputHistory, CheckLFMDlg, etMessagesWnd, UnitResources,
   ConvCodeTool, BasePkgManager, PackageDefs, PackageSystem, Designer, DesignerProcs;
 
 type
@@ -6438,12 +6438,15 @@ function FindBaseComponentClass(AnUnitInfo: TUnitInfo; const AComponentClassName
   DescendantClassName: string; out AComponentClass: TComponentClass): boolean;
 // returns false if an error occured
 // Important: returns true even if AComponentClass=nil
+var
+  ResFormat: TUnitResourcefileFormatClass;
 begin
   AComponentClass:=nil;
   // find the ancestor class
-  if AnUnitInfo.UnitResourceFileformat<>nil then
+  ResFormat:=AnUnitInfo.UnitResourceFileformat;
+  if ResFormat<>nil then
   begin
-    AComponentClass:=AnUnitInfo.UnitResourceFileformat.FindComponentClass(AComponentClassName);
+    AComponentClass:=ResFormat.FindComponentClass(AComponentClassName);
     if AComponentClass<>nil then
       exit(true);
   end;
@@ -6481,9 +6484,10 @@ function LoadAncestorDependencyHidden(AnUnitInfo: TUnitInfo;
   out AncestorClass: TComponentClass;
   out AncestorUnitInfo: TUnitInfo): TModalResult;
 var
-  AncsClsName, S: String;
+  AncestorClsName, S: String;
   CodeBuf: TCodeBuffer;
   GrandAncestorClass, DefAncestorClass: TComponentClass;
+  ResFormat: TUnitResourcefileFormatClass;
 begin
   AncestorClass:=nil;
   AncestorUnitInfo:=nil;
@@ -6496,34 +6500,30 @@ begin
     AnUnitInfo.Source:=CodeBuf;
   end;
 
-  S:=aComponentClassName;
-  repeat
-    if not CodeToolBoss.FindFormAncestor(AnUnitInfo.Source,S,AncsClsName,true) then
-      DebugLn('LoadAncestorDependencyHidden Filename="',AnUnitInfo.Filename,'" ClassName=',aComponentClassName,
-              '. Unable to find ancestor class: ',CodeToolBoss.ErrorMessage);
-    // try the base designer classes
-    if not FindBaseComponentClass(AnUnitInfo,AncsClsName,S,AncestorClass) then
-    begin
-      DebugLn(['LoadAncestorDependencyHidden FindUnitComponentClass failed for AncsClsName=',AncsClsName]);
-      exit(mrCancel);
-    end;
-    S:=AncsClsName;
-  until Assigned(AncestorClass);
+  if not CodeToolBoss.FindFormAncestor(AnUnitInfo.Source,aComponentClassName,
+                                       AncestorClsName,true) then
+    DebugLn('LoadAncestorDependencyHidden Filename="',AnUnitInfo.Filename,'" ClassName=',aComponentClassName,
+            '. Unable to find ancestor class: ',CodeToolBoss.ErrorMessage);
+  // try the base designer classes
+  if not FindBaseComponentClass(AnUnitInfo,AncestorClsName,aComponentClassName,
+                                AncestorClass) then
+  begin
+    DebugLn(['LoadAncestorDependencyHidden FindUnitComponentClass failed for AncestorClsName=',AncestorClsName]);
+    exit(mrCancel);
+  end;
 
   // try loading the ancestor first (unit, lfm and component instance)
-  if AnUnitInfo.UnitResourceFileformat<>nil then
-    DefAncestorClass:=AnUnitInfo.UnitResourceFileformat.DefaultComponentClass
+  ResFormat:=AnUnitInfo.UnitResourceFileformat;
+  if ResFormat<>nil then
+    DefAncestorClass:=ResFormat.DefaultComponentClass(aComponentClassName)
   else
-    DefAncestorClass:=nil;
-  // use TForm as default ancestor
-  if DefAncestorClass=nil then
     DefAncestorClass:=BaseFormEditor1.StandardDesignerBaseClasses[DesignerBaseClassId_TForm];
 
   if (AncestorClass=nil) then begin
     S:='';
     if DefAncestorClass<>nil then
       S:=Format(lisIgnoreUseAsAncestor, [DefAncestorClass.ClassName]);
-    Result:=LoadComponentDependencyHidden(AnUnitInfo,AncsClsName,OpenFlags,
+    Result:=LoadComponentDependencyHidden(AnUnitInfo,AncestorClsName,OpenFlags,
                       false,AncestorClass,AncestorUnitInfo,GrandAncestorClass,S);
     if Result<>mrOk then begin
       DebugLn(['LoadAncestorDependencyHidden DoLoadComponentDependencyHidden failed AnUnitInfo=',AnUnitInfo.Filename]);
@@ -6540,7 +6540,7 @@ begin
     end;
   end;
 
-  //DebugLn('LoadAncestorDependencyHidden Filename="',AnUnitInfo.Filename,'" AncsClsName=',AncsClsName,' AncestorClass=',dbgsName(AncestorClass));
+  //DebugLn('LoadAncestorDependencyHidden Filename="',AnUnitInfo.Filename,'" AncestorClsName=',AncestorClsName,' AncestorClass=',dbgsName(AncestorClass));
   if AncestorClass=nil then
     AncestorClass:=DefAncestorClass;
   Result:=mrOk;
@@ -7062,13 +7062,13 @@ begin
   AComponentClass:=nil;
   Quiet:=([ofProjectLoading,ofQuiet]*Flags<>[]);
   HideAbort:=not (ofProjectLoading in Flags);
-
+{  Will be checked in FindComponentClass()
   if not IsValidIdent(AComponentClassName) then
   begin
     DebugLn(['LoadComponentDependencyHidden invalid component class name "',AComponentClassName,'"']);
     exit(mrCancel);
   end;
-
+}
   // check for cycles
   if AnUnitInfo.LoadingComponent then begin
     Result:=IDEQuestionDialogAb(lisCodeTemplError,
diff --git a/packager/pkgmanager.pas b/packager/pkgmanager.pas
index c49a958a08..8e5cd18b2d 100644
--- a/packager/pkgmanager.pas
+++ b/packager/pkgmanager.pas
@@ -4453,7 +4453,7 @@ begin
   try
     Result:=GetUnitsAndDepsForComps(ComponentClasses, Dependencies, UnitNames);
     if Result<>mrOk then exit;
-
+    Assert(Assigned(UnitNames), 'TPkgManager.AddUnitDepsForCompClasses: UnitNames=Nil.');
     if (Dependencies<>nil) then
     begin
       Result:=FilterMissingDepsForUnit(UnitFilename,Dependencies,MissingDependencies);