diff --git a/ietf/api/__init__.py b/ietf/api/__init__.py
index e236347975..230f8339bd 100644
--- a/ietf/api/__init__.py
+++ b/ietf/api/__init__.py
@@ -62,14 +62,14 @@ def generate_cache_key(self, *args, **kwargs):
         # Use a list plus a ``.join()`` because it's faster than concatenation.
         return "%s:%s:%s:%s" % (self._meta.api_name, self._meta.resource_name, ':'.join(args), smooshed)
 
-    def _z_aware_fromisoformat(self, value):
-        """datetime.datetie.fromisoformat replacement that works with python < 3.11"""
+    def _z_aware_fromisoformat(self, value: str) -> datetime.datetime:
+        """datetime.datetime.fromisoformat replacement that works with python < 3.11"""
         if HAVE_BROKEN_FROMISOFORMAT:
             if value.upper().endswith("Z"):
                 value = value[:-1] + "+00:00"  # Z -> UTC
             elif re.match(r"[+-][0-9][0-9]$", value[-3:]):
                 value = value + ":00"  # -04 -> -04:00
-        return value
+        return datetime.datetime.fromisoformat(value)
 
     def filter_value_to_python(
         self, value, field_name, filters, filter_expr, filter_type