diff --git a/src/atrule.rs b/src/atrule.rs
index 9444283..1b45366 100644
--- a/src/atrule.rs
+++ b/src/atrule.rs
@@ -116,7 +116,7 @@ impl AtRule {
                 let u = UnknownAtRule {
                     name: name.clone(),
                     super_selector: Selector::new(),
-                    params,
+                    params: params.trim().to_owned(),
                     body,
                 };