diff --git a/app/MindWork AI Studio/Assistants/I18N/allTexts.lua b/app/MindWork AI Studio/Assistants/I18N/allTexts.lua
index ad6aac89..6ac89cdc 100644
--- a/app/MindWork AI Studio/Assistants/I18N/allTexts.lua	
+++ b/app/MindWork AI Studio/Assistants/I18N/allTexts.lua	
@@ -2344,6 +2344,9 @@ UI_TEXT_CONTENT["AISTUDIO::ASSISTANTS::VISUALBRIEFING::VISUALBRIEFINGASSISTANT::
 -- Please select a provider.
 UI_TEXT_CONTENT["AISTUDIO::ASSISTANTS::VISUALBRIEFING::VISUALBRIEFINGASSISTANT::T1809312323"] = "Please select a provider."
 
+-- Please add at least one source material file.
+UI_TEXT_CONTENT["AISTUDIO::ASSISTANTS::VISUALBRIEFING::VISUALBRIEFINGASSISTANT::T1957239290"] = "Please add at least one source material file."
+
 -- Cannot be opened
 UI_TEXT_CONTENT["AISTUDIO::ASSISTANTS::VISUALBRIEFING::VISUALBRIEFINGASSISTANT::T1981873292"] = "Cannot be opened"
 
diff --git a/app/MindWork AI Studio/Assistants/VisualBriefing/VisualBriefingAssistant.razor.Build.cs b/app/MindWork AI Studio/Assistants/VisualBriefing/VisualBriefingAssistant.razor.Build.cs
index 43e673e0..6a537fe4 100644
--- a/app/MindWork AI Studio/Assistants/VisualBriefing/VisualBriefingAssistant.razor.Build.cs	
+++ b/app/MindWork AI Studio/Assistants/VisualBriefing/VisualBriefingAssistant.razor.Build.cs	
@@ -24,6 +24,7 @@ public partial class VisualBriefingAssistant
         string.IsNullOrWhiteSpace(this.projectName) ||
         this.targetLanguage is CommonLanguages.OTHER && string.IsNullOrWhiteSpace(this.customTargetLanguage) ||
         this.protectionLevel is VisualBriefingProtectionLevel.OTHER && string.IsNullOrWhiteSpace(this.customProtectionLevel) ||
+        mode is not VisualBriefingEditMode.CHANGE_DESIGN && !this.HasSourceMaterial ||
         mode is VisualBriefingEditMode.CHANGE_DESIGN or VisualBriefingEditMode.UPDATE_CONTENT &&
         !this.SelectedVersionSupportsEdits ||
         mode is not VisualBriefingEditMode.CHANGE_DESIGN &&
diff --git a/app/MindWork AI Studio/Assistants/VisualBriefing/VisualBriefingAssistant.razor.Validation.cs b/app/MindWork AI Studio/Assistants/VisualBriefing/VisualBriefingAssistant.razor.Validation.cs
index 4178854f..3fbd4cd1 100644
--- a/app/MindWork AI Studio/Assistants/VisualBriefing/VisualBriefingAssistant.razor.Validation.cs	
+++ b/app/MindWork AI Studio/Assistants/VisualBriefing/VisualBriefingAssistant.razor.Validation.cs	
@@ -6,6 +6,9 @@ namespace AIStudio.Assistants.VisualBriefing;
 
 public partial class VisualBriefingAssistant
 {
+    /// <summary>Gets whether the briefing contains at least one actual source-material file.</summary>
+    private bool HasSourceMaterial => this.selectedBriefing?.Sources.Any(source => source.Kind is VisualBriefingSourceKind.SOURCE_MATERIAL) == true;
+
     /// <summary>Gets all current field, source, and revision issues shown below the actions.</summary>
     private IReadOnlyList<string> ValidationIssues
     {
@@ -20,6 +23,9 @@ public partial class VisualBriefingAssistant
 
             if (this.selectedBriefing is not null)
             {
+                if (!this.HasSourceMaterial)
+                    issues.Add(T("Please add at least one source material file."));
+
                 foreach (var source in this.selectedBriefing.Sources)
                 {
                     var fileName = Path.GetFileName(source.Path);
diff --git a/app/MindWork AI Studio/Assistants/VisualBriefing/VisualBriefingBuildOrchestrator.Inputs.cs b/app/MindWork AI Studio/Assistants/VisualBriefing/VisualBriefingBuildOrchestrator.Inputs.cs
index b99eeef0..b026c0ce 100644
--- a/app/MindWork AI Studio/Assistants/VisualBriefing/VisualBriefingBuildOrchestrator.Inputs.cs	
+++ b/app/MindWork AI Studio/Assistants/VisualBriefing/VisualBriefingBuildOrchestrator.Inputs.cs	
@@ -233,6 +233,26 @@ internal sealed partial class VisualBriefingBuildOrchestrator
                 "No provider is selected.");
     }
 
+    /// <summary>
+    /// Ensures content-generating builds have at least one source-material file.
+    /// </summary>
+    /// <param name="manifest">The briefing manifest.</param>
+    /// <param name="mode">The requested edit mode.</param>
+    private static void ValidateSourceMaterial(VisualBriefingManifest manifest, VisualBriefingEditMode mode)
+    {
+        if (mode is VisualBriefingEditMode.CHANGE_DESIGN or VisualBriefingEditMode.RECOMPILE ||
+            manifest.Sources.Any(source => source.Kind is VisualBriefingSourceKind.SOURCE_MATERIAL))
+        {
+            return;
+        }
+
+        throw new VisualBriefingBuildException(
+            VisualBriefingFailureCode.SOURCE_PREPARATION_FAILED,
+            VisualBriefingBuildStage.SOURCE_PREPARATION,
+            "Please add at least one source material file.",
+            "The briefing has no SOURCE_MATERIAL source.");
+    }
+
     /// <summary>
     /// Validates image-input capabilities for content analysis.
     /// </summary>
diff --git a/app/MindWork AI Studio/Assistants/VisualBriefing/VisualBriefingBuildOrchestrator.cs b/app/MindWork AI Studio/Assistants/VisualBriefing/VisualBriefingBuildOrchestrator.cs
index a036f34f..18d815da 100644
--- a/app/MindWork AI Studio/Assistants/VisualBriefing/VisualBriefingBuildOrchestrator.cs	
+++ b/app/MindWork AI Studio/Assistants/VisualBriefing/VisualBriefingBuildOrchestrator.cs	
@@ -99,6 +99,7 @@ internal sealed partial class VisualBriefingBuildOrchestrator
         try
         {
             ValidateProvider(provider);
+            ValidateSourceMaterial(manifest, mode);
             var parentContext = await this.LoadParentContextAsync(manifest, mode, parentRevisionId, token);
             VisualBriefingEvidenceArtifact? reusableEvidence = null;
             
diff --git a/app/MindWork AI Studio/Assistants/VisualBriefing/VisualBriefingStore.Versions.cs b/app/MindWork AI Studio/Assistants/VisualBriefing/VisualBriefingStore.Versions.cs
index beb678b3..1c18ba68 100644
--- a/app/MindWork AI Studio/Assistants/VisualBriefing/VisualBriefingStore.Versions.cs	
+++ b/app/MindWork AI Studio/Assistants/VisualBriefing/VisualBriefingStore.Versions.cs	
@@ -20,6 +20,12 @@ public sealed partial class VisualBriefingStore
         {
             var manifest = await this.LoadRequiredWithoutInitializeAsync(request.BriefingId, token);
             RefreshSourceStatuses(manifest);
+            if (request.EditMode is not (VisualBriefingEditMode.CHANGE_DESIGN or VisualBriefingEditMode.RECOMPILE) &&
+                manifest.Sources.All(source => source.Kind is not VisualBriefingSourceKind.SOURCE_MATERIAL))
+            {
+                return VisualBriefingRevisionResult.Failure("Please add at least one source material file.");
+            }
+
             var blockingSources = manifest.Sources
                 .Where(source => source.Status is VisualBriefingSourceStatus.UNREACHABLE or VisualBriefingSourceStatus.TRANSCRIPT_OUTDATED)
                 .ToArray();
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 7abca7f8..53877fe3 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	
@@ -2346,6 +2346,9 @@ UI_TEXT_CONTENT["AISTUDIO::ASSISTANTS::VISUALBRIEFING::VISUALBRIEFINGASSISTANT::
 -- Please select a provider.
 UI_TEXT_CONTENT["AISTUDIO::ASSISTANTS::VISUALBRIEFING::VISUALBRIEFINGASSISTANT::T1809312323"] = "Bitte wählen Sie einen Anbieter aus."
 
+-- Please add at least one source material file.
+UI_TEXT_CONTENT["AISTUDIO::ASSISTANTS::VISUALBRIEFING::VISUALBRIEFINGASSISTANT::T1957239290"] = "Bitte fügen Sie mindestens eine Quelldatei hinzu."
+
 -- Cannot be opened
 UI_TEXT_CONTENT["AISTUDIO::ASSISTANTS::VISUALBRIEFING::VISUALBRIEFINGASSISTANT::T1981873292"] = "Kann nicht geöffnet werden"
 
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 edf3c54c..27e64d11 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	
@@ -2346,6 +2346,9 @@ UI_TEXT_CONTENT["AISTUDIO::ASSISTANTS::VISUALBRIEFING::VISUALBRIEFINGASSISTANT::
 -- Please select a provider.
 UI_TEXT_CONTENT["AISTUDIO::ASSISTANTS::VISUALBRIEFING::VISUALBRIEFINGASSISTANT::T1809312323"] = "Please select a provider."
 
+-- Please add at least one source material file.
+UI_TEXT_CONTENT["AISTUDIO::ASSISTANTS::VISUALBRIEFING::VISUALBRIEFINGASSISTANT::T1957239290"] = "Please add at least one source material file."
+
 -- Cannot be opened
 UI_TEXT_CONTENT["AISTUDIO::ASSISTANTS::VISUALBRIEFING::VISUALBRIEFINGASSISTANT::T1981873292"] = "Cannot be opened"