diff --git a/ruian-swagger/requirements-slim.txt b/ruian-swagger/requirements-slim.txt
index ce8fa15..cd91974 100644
--- a/ruian-swagger/requirements-slim.txt
+++ b/ruian-swagger/requirements-slim.txt
@@ -16,3 +16,4 @@ dicttoxml~=1.7.4
 lat-lon-parser==1.2.0
 gunicorn==20.1.0
 Flask-Cors==3.0.10
+marshmallow>=3.26.2 # not directly required, pinned by Snyk to avoid a vulnerability