diff --git a/src/optional.rs b/src/optional.rs
index bd02ca6..42cb1eb 100644
--- a/src/optional.rs
+++ b/src/optional.rs
@@ -61,7 +61,7 @@ where
         D: serde::Deserializer<'de>,
     {
         let s: Option<String> = Deserialize::<'de>::deserialize(deserializer)?;
-        match s.as_deref() {
+        match s.as_deref().map(|s| s.trim()) {
             None | Some("") => Ok(Optional { inner: None }),
             Some(s) => T::from_str(&s)
                 .map_err(D::Error::custom)