diff --git a/src/gateway/mod.rs b/src/gateway/mod.rs
index 98965046a..d76a9e9c0 100644
--- a/src/gateway/mod.rs
+++ b/src/gateway/mod.rs
@@ -68,7 +68,10 @@ async fn security_headers_middleware(req: axum::extract::Request, next: Next) ->
         HeaderValue::from_static("nosniff"),
     );
     headers.insert(header::X_FRAME_OPTIONS, HeaderValue::from_static("DENY"));
-    headers.insert(header::CACHE_CONTROL, HeaderValue::from_static("no-store"));
+    // Only set Cache-Control if not already set by handler (e.g., SSE uses no-cache)
+    headers
+        .entry(header::CACHE_CONTROL)
+        .or_insert(HeaderValue::from_static("no-store"));
     headers.insert(header::X_XSS_PROTECTION, HeaderValue::from_static("0"));
     headers.insert(
         header::REFERRER_POLICY,
@@ -5772,4 +5775,39 @@ Reminder set successfully."#;
             "strict-origin-when-cross-origin"
         );
     }
+
+    #[tokio::test]
+    async fn security_headers_are_set_on_error_responses() {
+        use axum::body::Body;
+        use axum::http::{Request, StatusCode};
+        use tower::ServiceExt;
+
+        let app = Router::new()
+            .route(
+                "/error",
+                get(|| async { StatusCode::INTERNAL_SERVER_ERROR }),
+            )
+            .layer(axum::middleware::from_fn(
+                super::security_headers_middleware,
+            ));
+
+        let req = Request::builder()
+            .uri("/error")
+            .body(Body::empty())
+            .unwrap();
+
+        let response = app.oneshot(req).await.unwrap();
+        assert_eq!(response.status(), StatusCode::INTERNAL_SERVER_ERROR);
+        assert_eq!(
+            response
+                .headers()
+                .get(header::X_CONTENT_TYPE_OPTIONS)
+                .unwrap(),
+            "nosniff"
+        );
+        assert_eq!(
+            response.headers().get(header::X_FRAME_OPTIONS).unwrap(),
+            "DENY"
+        );
+    }
 }