diff --git a/web/src/endpoints/availability/post_new.rs b/web/src/endpoints/availability/post_new.rs
index 7e0602da..9e2f46df 100644
--- a/web/src/endpoints/availability/post_new.rs
+++ b/web/src/endpoints/availability/post_new.rs
@@ -26,9 +26,14 @@ pub async fn post(
         availability: None,
     };
 
+    let comment = form
+        .comment
+        .clone()
+        .and_then(|c| if !c.trim().is_empty() { Some(c) } else { None });
+
     let mut changeset = AvailabilityChangeset {
         time: (start, end),
-        comment: form.comment.clone(),
+        comment,
     };
 
     if let Err(e) = changeset.validate_with_context(&context).await {
diff --git a/web/src/endpoints/availability/post_update.rs b/web/src/endpoints/availability/post_update.rs
index 30a3a766..443f4864 100644
--- a/web/src/endpoints/availability/post_update.rs
+++ b/web/src/endpoints/availability/post_update.rs
@@ -29,6 +29,11 @@ pub async fn post(
     let start = form.startdate.and_time(form.starttime);
     let end = form.enddate.and_time(form.endtime);
 
+    let comment = form
+        .comment
+        .clone()
+        .and_then(|c| if !c.trim().is_empty() { Some(c) } else { None });
+
     let context = AvailabilityContext {
         pool: pool.get_ref(),
         user_id: user.id,
@@ -37,7 +42,7 @@ pub async fn post(
 
     let mut changeset = AvailabilityChangeset {
         time: (start, end),
-        comment: form.comment.clone(),
+        comment,
     };
 
     if let Err(e) = changeset.validate_with_context(&context).await {