diff --git a/backend/src/main/java/org/raddatz/familienarchiv/service/ThumbnailService.java b/backend/src/main/java/org/raddatz/familienarchiv/service/ThumbnailService.java
index 3b4cb48e..8fbf8d92 100644
--- a/backend/src/main/java/org/raddatz/familienarchiv/service/ThumbnailService.java
+++ b/backend/src/main/java/org/raddatz/familienarchiv/service/ThumbnailService.java
@@ -7,6 +7,7 @@ import org.apache.pdfbox.pdmodel.PDDocument;
 import org.apache.pdfbox.rendering.ImageType;
 import org.apache.pdfbox.rendering.PDFRenderer;
 import org.raddatz.familienarchiv.model.Document;
+import org.raddatz.familienarchiv.model.ThumbnailAspect;
 import org.raddatz.familienarchiv.repository.DocumentRepository;
 import org.springframework.beans.factory.annotation.Value;
 import org.springframework.stereotype.Service;
@@ -45,6 +46,9 @@ public class ThumbnailService {
     private static final int THUMBNAIL_WIDTH = 240;
     private static final float JPEG_QUALITY = 0.85f;
     private static final int PDF_RENDER_DPI = 100;
+    // Anything below this w/h ratio stays PORTRAIT — near-square A4 scans should
+    // render in the portrait tile rather than flipping to landscape at 1.01.
+    private static final float LANDSCAPE_THRESHOLD = 1.1f;
     private static final String PDF_CONTENT_TYPE = "application/pdf";
     private static final Set<String> IMAGE_CONTENT_TYPES =
             Set.of("image/jpeg", "image/png", "image/tiff");
@@ -83,7 +87,10 @@ public class ThumbnailService {
         }
 
         BufferedImage source = readSourceImage(doc, contentType);
-        if (source == null) return Outcome.FAILED;
+        if (source == null || source.getWidth() <= 0 || source.getHeight() <= 0) {
+            log.warn("Thumbnail source has invalid dimensions for doc={}", doc.getId());
+            return Outcome.FAILED;
+        }
 
         byte[] jpeg = encodeThumbnail(source, doc.getId());
         if (jpeg == null) return Outcome.FAILED;
@@ -91,7 +98,13 @@ public class ThumbnailService {
         String thumbnailKey = thumbnailKeyFor(doc.getId());
         if (!uploadToStorage(thumbnailKey, jpeg, doc.getId())) return Outcome.FAILED;
 
-        return persistThumbnailMetadata(doc, thumbnailKey);
+        ThumbnailAspect aspect = aspectOf(source);
+        return persistThumbnailMetadata(doc, thumbnailKey, aspect);
+    }
+
+    private static ThumbnailAspect aspectOf(BufferedImage source) {
+        float ratio = (float) source.getWidth() / source.getHeight();
+        return ratio > LANDSCAPE_THRESHOLD ? ThumbnailAspect.LANDSCAPE : ThumbnailAspect.PORTRAIT;
     }
 
     private static String thumbnailKeyFor(UUID documentId) {
@@ -138,10 +151,11 @@ public class ThumbnailService {
         }
     }
 
-    private Outcome persistThumbnailMetadata(Document doc, String thumbnailKey) {
+    private Outcome persistThumbnailMetadata(Document doc, String thumbnailKey, ThumbnailAspect aspect) {
         try {
             doc.setThumbnailKey(thumbnailKey);
             doc.setThumbnailGeneratedAt(LocalDateTime.now());
+            doc.setThumbnailAspect(aspect);
             documentRepository.save(doc);
             return Outcome.SUCCESS;
         } catch (Exception e) {
diff --git a/backend/src/test/java/org/raddatz/familienarchiv/service/ThumbnailServiceTest.java b/backend/src/test/java/org/raddatz/familienarchiv/service/ThumbnailServiceTest.java
index a2074891..df1f62b0 100644
--- a/backend/src/test/java/org/raddatz/familienarchiv/service/ThumbnailServiceTest.java
+++ b/backend/src/test/java/org/raddatz/familienarchiv/service/ThumbnailServiceTest.java
@@ -11,6 +11,7 @@ import org.junit.jupiter.api.Test;
 import org.mockito.ArgumentCaptor;
 import org.raddatz.familienarchiv.model.Document;
 import org.raddatz.familienarchiv.model.DocumentStatus;
+import org.raddatz.familienarchiv.model.ThumbnailAspect;
 import org.raddatz.familienarchiv.repository.DocumentRepository;
 import org.springframework.test.util.ReflectionTestUtils;
 import software.amazon.awssdk.core.sync.RequestBody;
@@ -167,6 +168,59 @@ class ThumbnailServiceTest {
         verify(documentRepository, never()).save(any());
     }
 
+    @Test
+    void generate_persistsPortraitAspect_forTypicalPortraitSourceImage() throws IOException {
+        // 600x800 → ratio w/h = 0.75 → below 1.1 threshold → PORTRAIT.
+        Document doc = makeDoc("image/png", "documents/portrait.png");
+        when(fileService.downloadFileStream(anyString()))
+                .thenReturn(new ByteArrayInputStream(createSamplePng(600, 800)));
+
+        ThumbnailService.Outcome outcome = thumbnailService.generate(doc);
+
+        assertThat(outcome).isEqualTo(ThumbnailService.Outcome.SUCCESS);
+        assertThat(doc.getThumbnailAspect()).isEqualTo(ThumbnailAspect.PORTRAIT);
+    }
+
+    @Test
+    void generate_persistsLandscapeAspect_whenWidthIsWellAboveHeight() throws IOException {
+        // 800x400 → ratio 2.0 → clearly above 1.1 → LANDSCAPE.
+        Document doc = makeDoc("image/jpeg", "documents/wide.jpg");
+        when(fileService.downloadFileStream(anyString()))
+                .thenReturn(new ByteArrayInputStream(createSampleJpeg(800, 400)));
+
+        ThumbnailService.Outcome outcome = thumbnailService.generate(doc);
+
+        assertThat(outcome).isEqualTo(ThumbnailService.Outcome.SUCCESS);
+        assertThat(doc.getThumbnailAspect()).isEqualTo(ThumbnailAspect.LANDSCAPE);
+    }
+
+    @Test
+    void generate_persistsPortraitAspect_whenSquareImage_belowLandscapeThreshold() throws IOException {
+        // 500x500 → ratio 1.0 → below 1.1 threshold → PORTRAIT (A4 scans often
+        // come in at near-square and we want them to live in the portrait tile).
+        Document doc = makeDoc("image/png", "documents/square.png");
+        when(fileService.downloadFileStream(anyString()))
+                .thenReturn(new ByteArrayInputStream(createSamplePng(500, 500)));
+
+        ThumbnailService.Outcome outcome = thumbnailService.generate(doc);
+
+        assertThat(outcome).isEqualTo(ThumbnailService.Outcome.SUCCESS);
+        assertThat(doc.getThumbnailAspect()).isEqualTo(ThumbnailAspect.PORTRAIT);
+    }
+
+    @Test
+    void generate_persistsPortraitAspect_justUnderLandscapeThreshold() throws IOException {
+        // 1099x1000 → ratio 1.099 → just under 1.1 threshold → PORTRAIT.
+        Document doc = makeDoc("image/png", "documents/near_threshold.png");
+        when(fileService.downloadFileStream(anyString()))
+                .thenReturn(new ByteArrayInputStream(createSamplePng(1099, 1000)));
+
+        ThumbnailService.Outcome outcome = thumbnailService.generate(doc);
+
+        assertThat(outcome).isEqualTo(ThumbnailService.Outcome.SUCCESS);
+        assertThat(doc.getThumbnailAspect()).isEqualTo(ThumbnailAspect.PORTRAIT);
+    }
+
     @Test
     void generate_returnsFailed_whenImageBytesAreCorrupt() throws IOException {
         // Truncated JPEG header — ImageIO returns null rather than throwing.