diff --git a/swh/web/common/service.py b/swh/web/common/service.py
--- a/swh/web/common/service.py
+++ b/swh/web/common/service.py
@@ -88,7 +88,7 @@
 
     """
     algo, hash = query.parse_hash(q)
-    found = storage.content_find({algo: hash})
+    found = _first_element(storage.content_find({algo: hash}))
     return {'found': converters.from_content(found),
             'algo': algo}
 
@@ -103,7 +103,7 @@
 
     """
     algo, hash = query.parse_hash(q)
-    found = storage.content_find({algo: hash})
+    found = _first_element(storage.content_find({algo: hash}))
     return {'found': found is not None}
 
 
@@ -119,7 +119,7 @@
     """
     algo, hash = query.parse_hash(q)
     if algo != 'sha1':
-        hashes = storage.content_find({algo: hash})
+        hashes = _first_element(storage.content_find({algo: hash}))
         if not hashes:
             return None
         return hashes['sha1']
@@ -690,13 +690,10 @@
 
     """
     sha1_git_bin = _to_sha1_bin(sha1_git)
-
     revision = _first_element(storage.revision_get([sha1_git_bin]))
     if not revision:
         raise NotFoundExc('Revision %s not found' % sha1_git)
-
     dir_sha1_git_bin = revision['directory']
-
     if dir_path:
         paths = dir_path.strip(os.path.sep).split(os.path.sep)
         entity = storage.directory_entry_get_by_path(
@@ -708,7 +705,6 @@
                 % (dir_path, sha1_git))
     else:
         entity = {'type': 'dir', 'target': dir_sha1_git_bin}
-
     if entity['type'] == 'dir':
         directory_entries = storage.directory_ls(entity['target']) or []
         return {'type': 'dir',
@@ -717,7 +713,14 @@
                 'content': list(map(converters.from_directory_entry,
                                     directory_entries))}
     elif entity['type'] == 'file':  # content
-        content = storage.content_find({'sha1_git': entity['target']})
+        content = _first_element(
+            storage.content_find({'sha1_git': entity['target']})
+            )
+        if not content:
+            raise NotFoundExc(
+                "Revision %s not found"
+                % (entity['target'])
+            )
         if with_data:
             c = _first_element(storage.content_get([content['sha1']]))
             content['data'] = c['data']
@@ -747,7 +750,7 @@
 
     """
     algo, hash = query.parse_hash(q)
-    c = storage.content_find({algo: hash})
+    c = _first_element(storage.content_find({algo: hash}))
     if not c:
         raise NotFoundExc('Content with %s checksum equals to %s not found!' %
                           (algo, hashutil.hash_to_hex(hash)))
diff --git a/swh/web/tests/common/test_service.py b/swh/web/tests/common/test_service.py
--- a/swh/web/tests/common/test_service.py
+++ b/swh/web/tests/common/test_service.py
@@ -295,7 +295,6 @@
             self, revision, unknown_revision):
         sha1_git_root = unknown_revision
         sha1_git = revision
-
         with self.assertRaises(NotFoundExc) as cm:
             service.lookup_revision_with_context(sha1_git_root, sha1_git)
         self.assertIn('Revision root %s not found' % sha1_git_root,
@@ -340,9 +339,23 @@
         self.assertIn('Revision %s not found' % unknown_revision,
                       cm.exception.args[0])
 
-    @given(revision())
-    def test_lookup_directory_with_revision_ko_path_to_nowhere(self, revision):
+    def test_lookup_directory_with_revision_unknown_content(self):
 
+        unknown_content_ = {
+            'sha1_git': '0cbad36778b71ee6a97e04e9e6201d2629f448d3'
+            }
+        revision_ = {'id': '5aad84493ee10c65fc28dfb1f9a4471917f902aa'}
+        sha1_git = revision_['id']
+        revision_['target'] = unknown_content_['sha1_git']
+        revision_['type'] = 'file'
+        with self.assertRaises(NotFoundExc) as cm:
+            service.lookup_directory_with_revision(sha1_git)
+        self.assertIn('Revision %s not found' % sha1_git,
+                      cm.exception.args[0])
+
+    @given(revision())
+    def test_lookup_directory_with_revision_ko_path_to_nowhere(
+            self, revision):
         invalid_path = 'path/to/something/unknown'
         with self.assertRaises(NotFoundExc) as cm:
             service.lookup_directory_with_revision(revision, invalid_path)