diff --git a/lcl/lazhelphtml.pas b/lcl/lazhelphtml.pas
index b46cba6d03..11ad304f82 100644
--- a/lcl/lazhelphtml.pas
+++ b/lcl/lazhelphtml.pas
@@ -265,8 +265,7 @@ begin
       Databases.SubstituteMacros(Result);
     //debugln('THTMLHelpDatabase.GetEffectiveBaseURL using DefaultBaseURL="',Result,'"');
   end;
-  if (Result<>'') and (Result[length(Result)]<>'/') then
-    Result:=Result+'/';
+  Result:=AppendURLPathDelim(Result);
 end;
 
 procedure THTMLHelpDatabase.Load(Storage: TConfigStorage);
diff --git a/lcl/lazhelpintf.pas b/lcl/lazhelpintf.pas
index 3b368a583f..4985b7d848 100644
--- a/lcl/lazhelpintf.pas
+++ b/lcl/lazhelpintf.pas
@@ -554,6 +554,7 @@ function ExtractURLDirectory(const URL: string): string;
 function TrimUrl(const URL: string): string;
 function TrimURLPath(const URLPath: string): string;
 function IsFileURL(const URL: string): boolean;
+function AppendURLPathDelim(const URLPath: string): string;
 
 procedure CreateListAndAdd(const AnObject: TObject; var List: TList;
   OnlyIfNotExists: boolean);
@@ -668,7 +669,7 @@ end;
 
 function URLFilenameIsAbsolute(const Filename: string): boolean;
 begin
-  Result:=FilenameIsUnixAbsolute(Filename);
+  Result:=FilenameIsAbsolute(SetDirSeparators(Filename));
 end;
 
 function FindURLPathStart(const URL: string): integer;
@@ -738,6 +739,12 @@ begin
           and (CompareByte(URL[1],'file://',7)=0);
 end;
 
+function AppendURLPathDelim(const URLPath: string): string;
+begin
+  if (Result<>'') and (Result[length(Result)]<>'/') then
+    Result:=Result+'/';
+end;
+
 function ExtractURLPath(const URL: string): string;
 var
   URLType, URLPath, URLParams: string;
@@ -1287,7 +1294,7 @@ begin
     if Result='' then exit;
     Result:=FilenameToURL(Result);
   end;
-  Result:=AppendPathDelim(Result);
+  Result:=AppendURLPathDelim(Result);
 end;
 
 function THelpDatabases.GetBaseDirectoryForBasePathObject(
@@ -1306,7 +1313,7 @@ begin
     Result:=THelpBasePathObject(BasePathObject).BasePath
   else
     Result:='';
-  Result:=AppendPathDelim(Result);
+  Result:=AppendURLPathDelim(Result);
 end;
 
 function THelpDatabases.FindViewer(const MimeType: string; var ErrMsg: string;