diff --git a/src/core/marker_utils.py b/src/core/marker_utils.py
index 6008ba03..feb42b5f 100644
--- a/src/core/marker_utils.py
+++ b/src/core/marker_utils.py
@@ -1,9 +1,13 @@
+import logging
 from io import BytesIO
 
+from django.core.exceptions import SuspiciousFileOperation
 from django.core.files.base import ContentFile
 from PIL import Image
 from pymarker import generate_marker_from_image
 
+log = logging.getLogger(__name__)
+
 BLACK_BORDER_PERCENTAGE = 20
 WHITE_BORDER_PERCENTAGE = 3
 INNER_BORDER_PERCENTAGE = 2
@@ -93,13 +97,21 @@ def generate_marker_variants(marker, inner_border=False):
         ]
     )
 
-    # Clean up the old source file if it moved to a new path
+    # Clean up the old source file if it moved to a new path.
+    # This is not merely tidying: until it is gone, the object sits in public
+    # storage under the name the uploader chose, so a failure here has to be
+    # visible rather than swallowed. It still must not fail the upload.
     if old_source_name and old_source_name != marker.source.name:
         try:
             if storage.exists(old_source_name):
                 storage.delete(old_source_name)
-        except Exception:
-            pass  # Non-critical cleanup
+        except (OSError, SuspiciousFileOperation):
+            log.exception(
+                "Could not delete the pre-rename marker source %s for marker %s; "
+                "it is still in storage under the uploader's own filename",
+                old_source_name,
+                marker.pk,
+            )
 
 
 def delete_marker_files(marker):
diff --git a/src/core/tests/test_marker_cleanup_logging.py b/src/core/tests/test_marker_cleanup_logging.py
new file mode 100644
index 00000000..2df75747
--- /dev/null
+++ b/src/core/tests/test_marker_cleanup_logging.py
@@ -0,0 +1,67 @@
+import io
+from unittest import mock
+
+from django.core.files.storage import default_storage
+from django.core.files.uploadedfile import SimpleUploadedFile
+from django.test import TestCase
+from django.urls import reverse
+from PIL import Image
+
+from core.models import Marker
+from users.models import User
+
+
+def upload_file(name="Minha imagem #1.png"):
+    buffer = io.BytesIO()
+    Image.new("RGB", (120, 120), "white").save(buffer, format="PNG")
+    buffer.seek(0)
+    return SimpleUploadedFile(name, buffer.read(), content_type="image/png")
+
+
+class TestMarkerCleanupLogging(TestCase):
+    """A failed cleanup leaves a user-named file public; it must be loud."""
+
+    def setUp(self):
+        self.username = "testuser"
+        self.password = "testpassword"
+        User.objects.create_user(username=self.username, password=self.password)
+        self.client.login(username=self.username, password=self.password)
+
+    def upload(self, title="Marker"):
+        return self.client.post(
+            reverse("marker-upload"),
+            {"source": upload_file(), "title": title, "author": "Test Author"},
+        )
+
+    def test_the_uploaded_file_is_renamed_away_from_the_users_filename(self):
+        self.upload("renamed")
+        marker = Marker.objects.get(title="renamed")
+
+        assert marker.source.name == f"markers/{marker.pk}/original.png"
+        assert "Minha imagem" not in marker.source.name
+
+    def test_a_failed_cleanup_is_logged_with_the_path_left_behind(self):
+        # Patch the storage instance the FileField actually uses, rather than a
+        # storage class: the test settings swap in an in-memory backend.
+        with mock.patch.object(
+            default_storage, "delete", side_effect=OSError("storage refused")
+        ):
+            with self.assertLogs("core.marker_utils", level="ERROR") as logs:
+                response = self.upload("cleanup failed")
+
+        assert response.status_code == 302, "the upload itself must still succeed"
+        assert Marker.objects.filter(title="cleanup failed").exists()
+        logged = "\n".join(logs.output)
+        # Django's get_valid_name sanitises the name but does not anonymise it:
+        # "Minha imagem #1.png" reaches storage as "Minha_imagem_1.png", still
+        # recognisably the uploader's, which is the whole point of #989.
+        assert "Minha_imagem" in logged, (
+            "the log must name the file still sitting in storage"
+        )
+        assert "storage refused" in logged, "the original exception must be included"
+
+    def test_a_successful_cleanup_logs_nothing(self):
+        with mock.patch("core.marker_utils.log") as logger:
+            self.upload("clean")
+
+        logger.exception.assert_not_called()