diff --git a/swh/indexer/origin_head.py b/swh/indexer/origin_head.py
--- a/swh/indexer/origin_head.py
+++ b/swh/indexer/origin_head.py
@@ -30,6 +30,8 @@
     def index(self, origin):
         origin_id = origin['id']
         latest_snapshot = self.storage.snapshot_get_latest(origin_id)
+        if latest_snapshot is None:
+            return None
         method = getattr(self, '_try_get_%s_head' % origin['type'], None)
         if method is None:
             method = self._try_get_head_generic
@@ -46,10 +48,9 @@
 
     def _try_get_vcs_head(self, snapshot):
         try:
-            if isinstance(snapshot, dict):
-                branches = snapshot['branches']
-                if branches[b'HEAD']['target_type'] == 'revision':
-                    return branches[b'HEAD']['target']
+            branches = snapshot['branches']
+            if branches[b'HEAD']['target_type'] == 'revision':
+                return branches[b'HEAD']['target']
         except KeyError:
             return None
 
@@ -111,8 +112,7 @@
     def _try_get_head_generic(self, snapshot):
         # Works on 'deposit', 'svn', and 'pypi'.
         try:
-            if isinstance(snapshot, dict):
-                branches = snapshot['branches']
+            branches = snapshot['branches']
         except KeyError:
             return None
         else:
diff --git a/swh/indexer/tests/test_origin_head.py b/swh/indexer/tests/test_origin_head.py
--- a/swh/indexer/tests/test_origin_head.py
+++ b/swh/indexer/tests/test_origin_head.py
@@ -55,6 +55,15 @@
                            b'\xd7}\xac\xefrm',
             'origin_id': origin_id}])
 
+    def test_vcs_missing_snapshot(self):
+        self.indexer.storage.origin_add([{
+            'type': 'git',
+            'url': 'https://github.com/SoftwareHeritage/swh-indexer',
+        }])
+        self.indexer.run(
+                ['git+https://github.com/SoftwareHeritage/swh-indexer'])
+        self.assertEqual(self.indexer.results, [])
+
     def test_ftp(self):
         self.indexer.run(
                 ['ftp+rsync://ftp.gnu.org/gnu/3dldf'])
@@ -65,6 +74,15 @@
                            b'\xcc\x1a\xb4`\x8c\x8by',
             'origin_id': origin_id}])
 
+    def test_ftp_missing_snapshot(self):
+        self.indexer.storage.origin_add([{
+            'type': 'ftp',
+            'url': 'rsync://ftp.gnu.org/gnu/foobar',
+        }])
+        self.indexer.run(
+                ['ftp+rsync://ftp.gnu.org/gnu/foobar'])
+        self.assertEqual(self.indexer.results, [])
+
     def test_deposit(self):
         self.indexer.run(
                 ['deposit+https://forge.softwareheritage.org/source/'
@@ -76,6 +94,15 @@
                            b'\xa6\xe9\x99\xb1\x9e]q\xeb',
             'origin_id': origin_id}])
 
+    def test_deposit_missing_snapshot(self):
+        self.indexer.storage.origin_add([{
+            'type': 'deposit',
+            'url': 'https://forge.softwareheritage.org/source/foobar',
+        }])
+        self.indexer.run(
+                ['deposit+https://forge.softwareheritage.org/source/foobar'])
+        self.assertEqual(self.indexer.results, [])
+
     def test_pypi(self):
         self.indexer.run(
                 ['pypi+https://pypi.org/project/limnoria/'])