diff --git a/swh/loader/package/debian/loader.py b/swh/loader/package/debian/loader.py
--- a/swh/loader/package/debian/loader.py
+++ b/swh/loader/package/debian/loader.py
@@ -8,17 +8,7 @@
 from os import path
 import re
 import subprocess
-from typing import (
-    Any,
-    Dict,
-    FrozenSet,
-    Iterator,
-    List,
-    Mapping,
-    Optional,
-    Sequence,
-    Tuple,
-)
+from typing import Any, Dict, Iterator, List, Mapping, Optional, Sequence, Tuple
 
 import attr
 from dateutil.parser import parse as parse_date
@@ -253,24 +243,38 @@
     if not artifacts_to_fetch:
         return None
 
-    def to_set(data: DebianPackageInfo) -> FrozenSet[Tuple[str, str, int]]:
-        return frozenset(
-            (name, meta.sha256, meta.size) for name, meta in data.files.items()
+    new_dsc_files = [
+        file for (name, file) in p_info.files.items() if name.endswith(".dsc")
+    ]
+
+    if len(new_dsc_files) != 1:
+        raise ValueError(
+            f"Expected exactly one new .dsc file for package {p_info.name}, "
+            f"got {len(new_dsc_files)}"
         )
 
-    # what we want to avoid downloading back if we have them already
-    set_new_artifacts = to_set(p_info)
+    new_dsc_sha256 = new_dsc_files[0].sha256
 
-    known_artifacts_revision_id = {}
     for rev_id, known_artifacts in known_package_artifacts.items():
         extrinsic = known_artifacts.get("extrinsic")
         if not extrinsic:
             continue
 
-        s = to_set(DebianPackageInfo.from_metadata(extrinsic["raw"], url=p_info.url))
-        known_artifacts_revision_id[s] = rev_id
+        known_p_info = DebianPackageInfo.from_metadata(extrinsic["raw"], url=p_info.url)
+        dsc = [
+            file for (name, file) in known_p_info.files.items() if name.endswith(".dsc")
+        ]
+
+        if len(dsc) != 1:
+            raise ValueError(
+                f"Expected exactly one known .dsc file for package {p_info.name}, "
+                f"got {len(dsc)}"
+            )
+
+        if new_dsc_sha256 == dsc[0].sha256:
+            return rev_id
 
-    return known_artifacts_revision_id.get(set_new_artifacts)
+    return None
 
 
 def uid_to_person(uid: str) -> Dict[str, str]:
diff --git a/swh/loader/package/debian/tests/test_debian.py b/swh/loader/package/debian/tests/test_debian.py
--- a/swh/loader/package/debian/tests/test_debian.py
+++ b/swh/loader/package/debian/tests/test_debian.py
@@ -497,3 +497,58 @@
     actual_revision = resolve_revision_from(known_package_artifacts, p_info)
 
     assert actual_revision == expected_revision_id
+
+
+def test_debian_resolve_revision_from_corrupt_known_artifact():
+    """To many or not enough .dsc files in the known_artifacts dict"""
+    artifact_metadata = PACKAGE_FILES
+    p_info = DebianPackageInfo.from_metadata(artifact_metadata, url=URL)
+    expected_revision_id = (
+        b"(\x07\xf5\xb3\xf8Ch\xb4\x88\x9a\x9a\xe8'\xfe\x85\x85O\xfe\xcf\x07"
+    )
+
+    files = dict(artifact_metadata["files"])
+    package_files = {
+        "name": PACKAGE_FILES["name"],
+        "version": PACKAGE_FILES["version"],
+        "files": files,
+    }
+
+    known_package_artifacts = {
+        expected_revision_id: {
+            "extrinsic": {"raw": package_files,},
+            # ... removed the unnecessary intermediary data
+        }
+    }
+
+    # Too many .dsc
+    files["another.dsc"] = files["cicero_0.7.2-3.dsc"]
+    with pytest.raises(ValueError, match="exactly one known .dsc"):
+        resolve_revision_from(known_package_artifacts, p_info)
+
+    # Not enough .dsc
+    del files["another.dsc"]
+    del files["cicero_0.7.2-3.dsc"]
+    with pytest.raises(ValueError, match="exactly one known .dsc"):
+        resolve_revision_from(known_package_artifacts, p_info)
+
+
+def test_debian_resolve_revision_from_corrupt_new_artifact():
+    artifact_metadata = PACKAGE_FILES
+
+    files = PACKAGE_FILES["files"]
+    files = {**files, "another.dsc": files["cicero_0.7.2-3.dsc"]}
+    artifact_metadata = {**PACKAGE_FILES, "files": files}
+
+    # Too many .dsc
+    files["another.dsc"] = files["cicero_0.7.2-3.dsc"]
+    p_info = DebianPackageInfo.from_metadata(artifact_metadata, url=URL)
+    with pytest.raises(ValueError, match="exactly one new .dsc"):
+        resolve_revision_from(PACKAGE_FILES, p_info)
+
+    # Not enough .dsc
+    del files["another.dsc"]
+    del files["cicero_0.7.2-3.dsc"]
+    p_info = DebianPackageInfo.from_metadata(artifact_metadata, url=URL)
+    with pytest.raises(ValueError, match="exactly one new .dsc"):
+        resolve_revision_from(PACKAGE_FILES, p_info)