diff --git a/app/MindWork AI Studio/Assistants/I18N/allTexts.lua b/app/MindWork AI Studio/Assistants/I18N/allTexts.lua
index 07569e094..da8c0c2a6 100644
--- a/app/MindWork AI Studio/Assistants/I18N/allTexts.lua	
+++ b/app/MindWork AI Studio/Assistants/I18N/allTexts.lua	
@@ -7621,6 +7621,9 @@ UI_TEXT_CONTENT["AISTUDIO::TOOLS::VALIDATION::FILEEXTENSIONVALIDATION::T29806295
 -- Images are not supported at this place
 UI_TEXT_CONTENT["AISTUDIO::TOOLS::VALIDATION::FILEEXTENSIONVALIDATION::T305247150"] = "Images are not supported at this place"
 
+-- This file format is not supported. Please convert the .doc file to .docx (e.g. with Microsoft Word).
+UI_TEXT_CONTENT["AISTUDIO::TOOLS::VALIDATION::FILEEXTENSIONVALIDATION::T3740637731"] = "This file format is not supported. Please convert the .doc file to .docx (e.g. with Microsoft Word)."
+
 -- Unsupported file type
 UI_TEXT_CONTENT["AISTUDIO::TOOLS::VALIDATION::FILEEXTENSIONVALIDATION::T4041351522"] = "Unsupported file type"
 
diff --git a/app/MindWork AI Studio/Plugins/languages/de-de-43065dbc-78d0-45b7-92be-f14c2926e2dc/plugin.lua b/app/MindWork AI Studio/Plugins/languages/de-de-43065dbc-78d0-45b7-92be-f14c2926e2dc/plugin.lua
index b65b6552b..132c2b72d 100644
--- a/app/MindWork AI Studio/Plugins/languages/de-de-43065dbc-78d0-45b7-92be-f14c2926e2dc/plugin.lua	
+++ b/app/MindWork AI Studio/Plugins/languages/de-de-43065dbc-78d0-45b7-92be-f14c2926e2dc/plugin.lua	
@@ -7611,6 +7611,9 @@ UI_TEXT_CONTENT["AISTUDIO::TOOLS::VALIDATION::FILEEXTENSIONVALIDATION::T13982828
 -- File has no extension
 UI_TEXT_CONTENT["AISTUDIO::TOOLS::VALIDATION::FILEEXTENSIONVALIDATION::T1555980031"] = "Datei hat keine Erweiterung"
 
+-- This file format is not supported.
+UI_TEXT_CONTENT["AISTUDIO::TOOLS::VALIDATION::FILEEXTENSIONVALIDATION::T2634293666"] = "Dieses Dateiformat wird nicht unterstützt. Bitte konvertieren Sie die .doc-Datei in .docx (z. B. mit Microsoft Word)."
+
 -- Audio files are not supported yet
 UI_TEXT_CONTENT["AISTUDIO::TOOLS::VALIDATION::FILEEXTENSIONVALIDATION::T2919730669"] = "Audio-Dateien werden noch nicht unterstützt."
 
diff --git a/app/MindWork AI Studio/Plugins/languages/en-us-97dfb1ba-50c4-4440-8dfa-6575daf543c8/plugin.lua b/app/MindWork AI Studio/Plugins/languages/en-us-97dfb1ba-50c4-4440-8dfa-6575daf543c8/plugin.lua
index 434c6aa31..ee4d24c7d 100644
--- a/app/MindWork AI Studio/Plugins/languages/en-us-97dfb1ba-50c4-4440-8dfa-6575daf543c8/plugin.lua	
+++ b/app/MindWork AI Studio/Plugins/languages/en-us-97dfb1ba-50c4-4440-8dfa-6575daf543c8/plugin.lua	
@@ -7623,6 +7623,9 @@ UI_TEXT_CONTENT["AISTUDIO::TOOLS::VALIDATION::FILEEXTENSIONVALIDATION::T29806295
 -- Images are not supported at this place
 UI_TEXT_CONTENT["AISTUDIO::TOOLS::VALIDATION::FILEEXTENSIONVALIDATION::T305247150"] = "Images are not supported at this place"
 
+-- This file format is not supported.
+UI_TEXT_CONTENT["AISTUDIO::TOOLS::VALIDATION::FILEEXTENSIONVALIDATION::T1506058512"] = "This file format is not supported. Please convert the .doc file to .docx (e.g. with Microsoft Word)."
+
 -- Unsupported file type
 UI_TEXT_CONTENT["AISTUDIO::TOOLS::VALIDATION::FILEEXTENSIONVALIDATION::T4041351522"] = "Unsupported file type"
 
@@ -7672,4 +7675,4 @@ UI_TEXT_CONTENT["AISTUDIO::TOOLS::WORKSPACEBEHAVIOUR::T1307384014"] = "Unnamed w
 UI_TEXT_CONTENT["AISTUDIO::TOOLS::WORKSPACEBEHAVIOUR::T2244038752"] = "Delete Chat"
 
 -- Unnamed chat
-UI_TEXT_CONTENT["AISTUDIO::TOOLS::WORKSPACEBEHAVIOUR::T3310482275"] = "Unnamed chat"
+UI_TEXT_CONTENT["AISTUDIO::TOOLS::WORKSPACEBEHAVIOUR::T3310482275"] = "Unnamed chat"
\ No newline at end of file
diff --git a/app/MindWork AI Studio/Tools/Rust/FileTypes.cs b/app/MindWork AI Studio/Tools/Rust/FileTypes.cs
index 87a551b2d..413e83ce9 100644
--- a/app/MindWork AI Studio/Tools/Rust/FileTypes.cs	
+++ b/app/MindWork AI Studio/Tools/Rust/FileTypes.cs	
@@ -45,7 +45,7 @@ public static class FileTypes
     // Document hierarchy
     public static readonly FileTypeFilter PDF         = FileTypeFilter.Leaf("PDF", "pdf");
     public static readonly FileTypeFilter TEXT        = FileTypeFilter.Leaf(TB("Text"), "txt", "md", "rtf");
-    public static readonly FileTypeFilter MS_WORD     = FileTypeFilter.Leaf("Microsoft Word", "docx", "doc");
+    public static readonly FileTypeFilter MS_WORD     = FileTypeFilter.Leaf("Microsoft Word", "docx");
     public static readonly FileTypeFilter WORD        = FileTypeFilter.Composite("Word", ["odt"], MS_WORD);
     public static readonly FileTypeFilter EXCEL       = FileTypeFilter.Leaf("Excel", "xls", "xlsx");
     public static readonly FileTypeFilter POWER_POINT = FileTypeFilter.Leaf("PowerPoint", "ppt", "pptx");
diff --git a/app/MindWork AI Studio/Tools/Validation/FileExtensionValidation.cs b/app/MindWork AI Studio/Tools/Validation/FileExtensionValidation.cs
index efecce3de..2251ecd5a 100644
--- a/app/MindWork AI Studio/Tools/Validation/FileExtensionValidation.cs	
+++ b/app/MindWork AI Studio/Tools/Validation/FileExtensionValidation.cs	
@@ -43,6 +43,14 @@ public enum UseCase
     /// <returns>True if valid, false if invalid (error/warning already sent via MessageBus).</returns>
     public static async Task<bool> IsExtensionValidWithNotifyAsync(UseCase useCae, string filePath, bool validateMediaFileTypes = true, Settings.Provider? provider = null)
     {
+        if (string.Equals(Path.GetExtension(filePath), ".doc", StringComparison.OrdinalIgnoreCase))
+        {
+            await MessageBus.INSTANCE.SendWarning(new(
+                Icons.Material.Filled.Description,
+                TB("This file format is not supported. Please convert the .doc file to .docx (e.g. with Microsoft Word).")));
+            return false;
+        }
+
         if (FileTypes.IsAllowedPath(filePath, FileTypes.EXECUTABLES))
         {
             await MessageBus.INSTANCE.SendError(new(
@@ -138,4 +146,4 @@ await MessageBus.INSTANCE.SendError(new(
 
         return true;
     }
-}
+}
\ No newline at end of file
diff --git a/app/MindWork AI Studio/wwwroot/changelog/v26.4.1.md b/app/MindWork AI Studio/wwwroot/changelog/v26.4.1.md
index 3ff00c6ab..8b4c23e0b 100644
--- a/app/MindWork AI Studio/wwwroot/changelog/v26.4.1.md	
+++ b/app/MindWork AI Studio/wwwroot/changelog/v26.4.1.md	
@@ -37,6 +37,7 @@
 - Fixed an issue where file and folder selection dialogs could open more than once on Windows. Thanks to Bernhard for reporting this bug.
 - Fixed an issue where exporting to Word could fail when the message contained certain formatting.
 - Fixed security issues in the native app runtime by strengthening how AI Studio creates and protects the secret values used for its internal secure connection.
+- Fixed an issue by no longer accepting .doc files. Users will now receive an appropriate error message when attempting to upload them. Thanks to Bernhard for reporting this issue.
 - Updated several security-sensitive Rust dependencies in the native runtime to address known vulnerabilities.
 - Updated .NET to v9.0.15
 - Updated dependencies
\ No newline at end of file