diff --git a/CHANGELOG.md b/CHANGELOG.md
index 23076680df..a109691307 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -9,6 +9,7 @@
 
 **Bug Fixes**:
 
+- Deny backslashes in release names. ([#904](https://github.com/getsentry/relay/pull/904))
 - Fix a problem with Data Scrubbing source names (PII selectors) that caused `$frame.abs_path` to match, but not `$frame.abs_path || **` or `$frame.abs_path && **`. ([#932](https://github.com/getsentry/relay/pull/932))
 - Make username pii-strippable. ([#935](https://github.com/getsentry/relay/pull/935))
 - Respond with `400 Bad Request` and an error message `"empty envelope"` instead of `429` when envelopes without items are sent to the envelope endpoint. ([#937](https://github.com/getsentry/relay/pull/937))
diff --git a/py/CHANGELOG.md b/py/CHANGELOG.md
index 6b0812b4ae..68e2884ab3 100644
--- a/py/CHANGELOG.md
+++ b/py/CHANGELOG.md
@@ -2,6 +2,7 @@
 
 ## Unreleased
 
+- Deny backslashes in release names. ([#904](https://github.com/getsentry/relay/pull/904))
 - Remove dependencies on `openssl` and `zlib`. ([#914](https://github.com/getsentry/relay/pull/914))
 
 ## 0.8.3
diff --git a/relay-general/src/protocol/event.rs b/relay-general/src/protocol/event.rs
index a5a8108dd0..5f8c126642 100644
--- a/relay-general/src/protocol/event.rs
+++ b/relay-general/src/protocol/event.rs
@@ -310,7 +310,7 @@ pub struct Event {
     /// can be the git SHA for the given project, or a product identifier with a semantic version.
     #[metastructure(
         max_chars = "tag_value",  // release ends in tag
-        deny_chars = "\r\n\x0c\t/",
+        deny_chars = "\r\n\x0c\t/\\",
         required = "false",
         trim_whitespace = "true",
         nonempty = "true",