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 90b0e8c8..a2074891 100644
--- a/backend/src/test/java/org/raddatz/familienarchiv/service/ThumbnailServiceTest.java
+++ b/backend/src/test/java/org/raddatz/familienarchiv/service/ThumbnailServiceTest.java
@@ -167,6 +167,38 @@ class ThumbnailServiceTest {
         verify(documentRepository, never()).save(any());
     }
 
+    @Test
+    void generate_returnsFailed_whenImageBytesAreCorrupt() throws IOException {
+        // Truncated JPEG header — ImageIO returns null rather than throwing.
+        // Without the corrupt-image guard this would later NPE inside the aspect /
+        // dimension computation in scaleToWidth.
+        Document doc = makeDoc("image/jpeg", "documents/corrupt.jpg");
+        byte[] truncated = new byte[]{(byte) 0xFF, (byte) 0xD8, (byte) 0xFF, (byte) 0xE0};
+        when(fileService.downloadFileStream(anyString()))
+                .thenReturn(new ByteArrayInputStream(truncated));
+
+        ThumbnailService.Outcome outcome = thumbnailService.generate(doc);
+
+        assertThat(outcome).isEqualTo(ThumbnailService.Outcome.FAILED);
+        verifyNoInteractions(s3Client);
+        verify(documentRepository, never()).save(any());
+    }
+
+    @Test
+    void generate_returnsFailed_whenPdfBytesAreCorrupt() throws IOException {
+        // "PDF" header but no body — PDFBox throws IOException while loading.
+        Document doc = makeDoc("application/pdf", "documents/corrupt.pdf");
+        byte[] fakePdf = "%PDF-1.4\n".getBytes();
+        when(fileService.downloadFileStream(anyString()))
+                .thenReturn(new ByteArrayInputStream(fakePdf));
+
+        ThumbnailService.Outcome outcome = thumbnailService.generate(doc);
+
+        assertThat(outcome).isEqualTo(ThumbnailService.Outcome.FAILED);
+        verifyNoInteractions(s3Client);
+        verify(documentRepository, never()).save(any());
+    }
+
     @Test
     void generate_returnsFailed_whenPersistThrows_butUploadSucceeded() throws IOException {
         // Covers the "orphan thumbnail" edge case: S3 upload succeeded but the