diff --git a/rust/src/events/internal_metadata.rs b/rust/src/events/internal_metadata.rs
index fa40fdcfad..38c6601d4f 100644
--- a/rust/src/events/internal_metadata.rs
+++ b/rust/src/events/internal_metadata.rs
@@ -55,6 +55,7 @@ enum EventInternalMetadataData {
     SoftFailed(bool),
     ProactivelySend(bool),
     PolicyServerSpammy(bool),
+    SpamCheckerSpammy(bool),
     Redacted(bool),
     TxnId(Box<str>),
     TokenId(i64),
@@ -104,6 +105,13 @@ impl EventInternalMetadataData {
                     .to_owned()
                     .into_any(),
             ),
+            EventInternalMetadataData::SpamCheckerSpammy(o) => (
+                pyo3::intern!(py, "spam_checker_spammy"),
+                o.into_pyobject(py)
+                    .unwrap_infallible()
+                    .to_owned()
+                    .into_any(),
+            ),
             EventInternalMetadataData::Redacted(o) => (
                 pyo3::intern!(py, "redacted"),
                 o.into_pyobject(py)
@@ -168,6 +176,11 @@ impl EventInternalMetadataData {
                     .extract()
                     .with_context(|| format!("'{key_str}' has invalid type"))?,
             ),
+            "spam_checker_spammy" => EventInternalMetadataData::SpamCheckerSpammy(
+                value
+                    .extract()
+                    .with_context(|| format!("'{key_str}' has invalid type"))?,
+            ),
             "redacted" => EventInternalMetadataData::Redacted(
                 value
                     .extract()
@@ -451,6 +464,17 @@ impl EventInternalMetadata {
         set_property!(self, PolicyServerSpammy, obj);
     }
 
+    #[getter]
+    fn get_spam_checker_spammy(&self) -> PyResult<bool> {
+        Ok(get_property_opt!(self, SpamCheckerSpammy)
+            .copied()
+            .unwrap_or(false))
+    }
+    #[setter]
+    fn set_spam_checker_spammy(&mut self, obj: bool) {
+        set_property!(self, SpamCheckerSpammy, obj);
+    }
+
     #[getter]
     fn get_redacted(&self) -> PyResult<bool> {
         let bool = get_property!(self, Redacted)?;
diff --git a/synapse/synapse_rust/events.pyi b/synapse/synapse_rust/events.pyi
index 0add391c65..9fcbe0f5d6 100644
--- a/synapse/synapse_rust/events.pyi
+++ b/synapse/synapse_rust/events.pyi
@@ -36,6 +36,19 @@ class EventInternalMetadata:
     policy_server_spammy: bool
     """whether the policy server indicated that this event is spammy"""
 
+    spam_checker_spammy: bool
+    """Whether a spam checker module indicated that this event is spammy
+
+    Note that spam checkers also cause the event to be marked as soft-failed.
+
+    This flags exists for two reasons:
+        1. as debugging information
+        2. to prevent the soft-failed re-evaluation of spammy events
+           (the re-evaluation behaviour originates from MSC4354 Sticky Events)
+
+    Note that historical spammy events won't have this flag.
+    """
+
     txn_id: str
     """The transaction ID, if it was set when the event was created."""
     token_id: int