diff --git a/rust/src/push/evaluator.rs b/rust/src/push/evaluator.rs
index 93ca7bae5569..1f26f667bc02 100644
--- a/rust/src/push/evaluator.rs
+++ b/rust/src/push/evaluator.rs
@@ -87,7 +87,7 @@ pub struct PushRuleEvaluator {
 
     /// The related events, indexed by relation type. Flattened in the same manner as
     /// `flattened_keys`.
-    related_events_flattened: BTreeMap<String, BTreeMap<String, String>>,
+    related_events_flattened: BTreeMap<String, BTreeMap<String, SimpleJsonValue>>,
 
     /// If msc3664, push rules for related events, is enabled.
     related_event_match_enabled: bool,
@@ -116,7 +116,7 @@ impl PushRuleEvaluator {
         room_member_count: u64,
         sender_power_level: Option<i64>,
         notification_power_levels: BTreeMap<String, i64>,
-        related_events_flattened: BTreeMap<String, BTreeMap<String, String>>,
+        related_events_flattened: BTreeMap<String, BTreeMap<String, SimpleJsonValue>>,
         related_event_match_enabled: bool,
         room_version_feature_flags: Vec<String>,
         msc3931_enabled: bool,
@@ -441,7 +441,7 @@ impl PushRuleEvaluator {
             return Ok(false);
         };
 
-        let haystack = if let Some(haystack) = event.get(&**key) {
+        let haystack = if let Some(SimpleJsonValue::Str(haystack)) = event.get(&**key) {
             haystack
         } else {
             return Ok(false);
diff --git a/stubs/synapse/synapse_rust/push.pyi b/stubs/synapse/synapse_rust/push.pyi
index 20fafce8f064..0fc2f703f2e8 100644
--- a/stubs/synapse/synapse_rust/push.pyi
+++ b/stubs/synapse/synapse_rust/push.pyi
@@ -62,7 +62,7 @@ class PushRuleEvaluator:
         room_member_count: int,
         sender_power_level: Optional[int],
         notification_power_levels: Mapping[str, int],
-        related_events_flattened: Mapping[str, Mapping[str, str]],
+        related_events_flattened: Mapping[str, Mapping[str, SimpleJsonValue]],
         related_event_match_enabled: bool,
         room_version_feature_flags: Tuple[str, ...],
         msc3931_enabled: bool,
diff --git a/synapse/push/bulk_push_rule_evaluator.py b/synapse/push/bulk_push_rule_evaluator.py
index 01d43db3b5df..8238381c3bc6 100644
--- a/synapse/push/bulk_push_rule_evaluator.py
+++ b/synapse/push/bulk_push_rule_evaluator.py
@@ -235,13 +235,15 @@ async def _get_power_levels_and_sender_level(
 
         return pl_event.content if pl_event else {}, sender_level
 
-    async def _related_events(self, event: EventBase) -> Dict[str, Dict[str, str]]:
+    async def _related_events(
+        self, event: EventBase
+    ) -> Dict[str, Dict[str, SimpleJsonValue]]:
         """Fetches the related events for 'event'. Sets the im.vector.is_falling_back key if the event is from a fallback relation
 
         Returns:
             Mapping of relation type to flattened events.
         """
-        related_events: Dict[str, Dict[str, str]] = {}
+        related_events: Dict[str, Dict[str, SimpleJsonValue]] = {}
         if self._related_event_match_enabled:
             related_event_id = event.content.get("m.relates_to", {}).get("event_id")
             relation_type = event.content.get("m.relates_to", {}).get("rel_type")