diff --git a/crates/tranquil-oauth/src/client.rs b/crates/tranquil-oauth/src/client.rs
index 3cabd23..b9d9f07 100644
--- a/crates/tranquil-oauth/src/client.rs
+++ b/crates/tranquil-oauth/src/client.rs
@@ -635,11 +635,6 @@ fn validate_client_assertion_times(iat: i64, exp: Option<i64>, now: i64) -> Resu
                 "client_assertion has expired".to_string(),
             ));
         }
-        if exp > now + 300 {
-            return Err(OAuthError::InvalidClient(
-                "client_assertion lifetime is too long".to_string(),
-            ));
-        }
     }
     Ok(())
 }
@@ -883,6 +878,7 @@ mod tests {
 
         assert!(validate_client_assertion_times(now, None, now).is_ok());
         assert!(validate_client_assertion_times(now, Some(now + 60), now).is_ok());
+        assert!(validate_client_assertion_times(now, Some(now + 600), now).is_ok());
         assert!(validate_client_assertion_times(now - 61, None, now).is_err());
         assert!(validate_client_assertion_times(now, Some(now - 1), now).is_err());
     }