diff --git a/kinto/core/resource/__init__.py b/kinto/core/resource/__init__.py
index f8aaa7b15..da447642e 100644
--- a/kinto/core/resource/__init__.py
+++ b/kinto/core/resource/__init__.py
@@ -665,7 +665,7 @@ def delete(self):
         obj = self._get_object_or_404(self.object_id)
         self._raise_412_if_modified(obj)
 
-        # Retreive the last_modified information from a querystring if present.
+        # Retrieve the last_modified information from a querystring if present.
         last_modified = self.request.validated["querystring"].get("last_modified")
 
         # If less or equal than current object. Ignore it.
@@ -1060,7 +1060,8 @@ def _extract_filters(self):
         """Extracts filters from QueryString parameters."""
 
         def is_valid_timestamp(value):
-            return isinstance(value, int) or re.match(r'^"?\d+"?$', str(value))
+            # Is either integer, or integer as string, or integer between 2 quotes.
+            return isinstance(value, int) or re.match(r'^(\d+)$|^("\d+")$', str(value))
 
         queryparams = self.request.validated["querystring"]
 
diff --git a/tests/core/resource/test_filter.py b/tests/core/resource/test_filter.py
index d34eb8f0a..1ccd14ac3 100644
--- a/tests/core/resource/test_filter.py
+++ b/tests/core/resource/test_filter.py
@@ -92,6 +92,10 @@ def test_filter_raises_error_if_last_modified_value_is_not_int(self):
         self.validated["querystring"] = {"lt_last_modified": bad_value}
         self.assertRaises(httpexceptions.HTTPBadRequest, self.resource.plural_get)
 
+    def test_filter_raises_error_if_last_modified_value_has_malformed_quotes(self):
+        self.validated["querystring"] = {"last_modified": '123"'}
+        self.assertRaises(httpexceptions.HTTPBadRequest, self.resource.plural_get)
+
     def test_filter_works_with_since_none(self):
         self.validated["querystring"] = {"_since": None}
         result = self.resource.plural_get()