diff --git a/crates/api_crud/src/post/create.rs b/crates/api_crud/src/post/create.rs
index ff684094b..881eda4d0 100644
--- a/crates/api_crud/src/post/create.rs
+++ b/crates/api_crud/src/post/create.rs
@@ -57,10 +57,12 @@ pub async fn create_post(
 
   let data_url = data.url.as_ref();
   let url = data_url.map(clean_url_params); // TODO no good way to handle a "clear"
+  let custom_thumbnail = data.custom_thumbnail.as_ref().map(clean_url_params);
 
   is_valid_post_title(&data.name)?;
   is_valid_body_field(&body, true)?;
-  check_url_scheme(&data.url)?;
+  check_url_scheme(&url)?;
+  check_url_scheme(&custom_thumbnail)?;
 
   check_community_user_action(
     &local_user_view.person,
@@ -87,7 +89,7 @@ pub async fn create_post(
   // Fetch post links and pictrs cached image
   let metadata = fetch_link_metadata_opt(url.as_ref(), true, &context).await;
   let url = proxy_image_link_opt_apub(url, &context).await?;
-  let thumbnail_url = data.custom_thumbnail.or(metadata.thumbnail);
+  let thumbnail_url = custom_thumbnail.map(Into::into).or(metadata.thumbnail);
 
   // Only need to check if language is allowed in case user set it explicitly. When using default
   // language, it already only returns allowed languages.
diff --git a/crates/api_crud/src/post/update.rs b/crates/api_crud/src/post/update.rs
index 3198aa2d1..e7d7f7c6f 100644
--- a/crates/api_crud/src/post/update.rs
+++ b/crates/api_crud/src/post/update.rs
@@ -43,6 +43,7 @@ pub async fn update_post(
   // TODO No good way to handle a clear.
   // Issue link: https://github.com/LemmyNet/lemmy/issues/2287
   let url = data.url.as_ref().map(clean_url_params);
+  let custom_thumbnail = data.custom_thumbnail.as_ref().map(clean_url_params);
 
   let slur_regex = local_site_to_slur_regex(&local_site);
   check_slurs_opt(&data.name, &slur_regex)?;
@@ -53,7 +54,8 @@ pub async fn update_post(
   }
 
   is_valid_body_field(&body, true)?;
-  check_url_scheme(&data.url)?;
+  check_url_scheme(&url)?;
+  check_url_scheme(&custom_thumbnail)?;
 
   let post_id = data.post_id;
   let orig_post = Post::read(&mut context.pool(), post_id).await?;
@@ -78,7 +80,7 @@ pub async fn update_post(
         Some(metadata.opengraph_data.title),
         Some(metadata.opengraph_data.description),
         Some(metadata.opengraph_data.embed_video_url),
-        Some(data.custom_thumbnail.or(metadata.thumbnail)),
+        Some(custom_thumbnail.map(Into::into).or(metadata.thumbnail)),
       )
     }
     _ => Default::default(),