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']
@@ -690,25 +690,20 @@
 
     """
     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(
             dir_sha1_git_bin, list(map(lambda p: p.encode('utf-8'), paths)))
-
         if not entity:
             raise NotFoundExc(
                 "Directory or File '%s' pointed to by revision %s not found"
                 % (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 +712,14 @@
                 '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(
+                "Content not found for revision %s"
+                % (sha1_git)
+            )
         if with_data:
             c = _first_element(storage.content_get([content['sha1']]))
             content['data'] = c['data']
@@ -747,7 +749,7 @@
 
     """
     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
@@ -11,6 +11,7 @@
 from hypothesis import given
 
 from swh.model.hashutil import hash_to_bytes, hash_to_hex
+from swh.model import from_disk
 
 from swh.web.common import service
 from swh.web.common.exc import BadInputExc, NotFoundExc
@@ -296,7 +297,6 @@
             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,
@@ -341,9 +341,57 @@
         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):
+    @given(revision(), unknown_content())
+    def test_lookup_directory_with_revision_unknown_content(
+            self, revision, unknown_content):
+        # First retrieve a known directory
+        sha1_git_bin = service._to_sha1_bin(revision)
+        revision_ = service._first_element(
+            self.storage.revision_get([sha1_git_bin])
+            )
+        # Get a directory path from memory
+        dir_path = [e for e in self.directory_ls(revision_['directory'])
+                    if e['type'] == 'file']
+        dir_path = dir_path[0]['name']
+        # Now modify the revision as follows
+        # A revision that points to a known directory
+        # Which points to unknown content
+        revision_['type'] = 'file'
+        revision_['id'] = service._to_sha1_bin(
+            revision[0:len(revision)-2]+"00"
+            )
+        revision_['directory'] = service._to_sha1_bin(
+            revision[0:len(revision)-2]+"88"
+            )
+        # A directory that points to unknown content
+        dir = {'id': service._to_sha1_bin(
+            revision[0:len(revision)-2]+"88"
+            ),
+            'entries': [{
+                    'name': bytes(dir_path.encode('utf-8')),
+                    'type': 'file',
+                    'target': service._to_sha1_bin(
+                        unknown_content['sha1_git']
+                        ),
+                    'perms': from_disk.DentryPerms.content
+            }]
+            }
+        # Add the directory and revision in mem
+        self.storage.directory_add([dir])
+        self.storage.revision_add([revision_])
 
+        with self.assertRaises(NotFoundExc) as cm:
+            service.lookup_directory_with_revision(
+                (
+                    revision[0:len(revision)-2]+"00"), dir_path
+                )
+        self.assertIn('Content not found for revision %s' %
+                      revision[0:len(revision)-2]+"00",
+                      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)