diff --git a/Cargo.toml b/Cargo.toml
index ab0c9c23..02284269 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -54,6 +54,8 @@ chrono = "0.4"
 
 itertools = "0.14.0"
 
+strsim = "0.10.0"
+
 [dev-dependencies]
 insta = "1.26"
 derive_builder = "0.20.0"
diff --git a/src/bors/handlers/review.rs b/src/bors/handlers/review.rs
index 36dbd6eb..e8796746 100644
--- a/src/bors/handlers/review.rs
+++ b/src/bors/handlers/review.rs
@@ -30,7 +30,16 @@ pub(super) async fn command_approve(
     };
     let approver = match approver {
         Approver::Myself => author.username.clone(),
-        Approver::Specified(approver) => approver.clone(),
+        Approver::Specified(approver) => {
+            if let Some(error_comment) = repo_state.client.validate_reviewers(approver).await? {
+                repo_state
+                    .client
+                    .post_comment(pr.number, error_comment)
+                    .await?;
+                return Ok(());
+            }
+            approver.clone()
+        }
     };
     db.approve(repo_state.repository(), pr.number, approver.as_str())
         .await?;
@@ -274,6 +283,21 @@ mod tests {
             .await;
     }
 
+    #[sqlx::test]
+    async fn approve_empty_reviewer_in_list(pool: sqlx::PgPool) {
+        BorsBuilder::new(pool)
+            .world(create_world_with_approve_config())
+            .run_test(|mut tester| async {
+                tester.post_comment("@bors r=user1,,user2").await?;
+                assert_eq!(
+                    tester.get_comment().await?,
+                    "Error: Empty reviewer name provided. Use r=username to specify a reviewer."
+                );
+                Ok(tester)
+            })
+            .await;
+    }
+
     #[sqlx::test]
     async fn insufficient_permission_approve(pool: sqlx::PgPool) {
         let world = World::default();
diff --git a/src/github/api/client.rs b/src/github/api/client.rs
index 23cef28a..be58c3c9 100644
--- a/src/github/api/client.rs
+++ b/src/github/api/client.rs
@@ -1,6 +1,7 @@
 use anyhow::Context;
 use octocrab::models::{App, Repository};
 use octocrab::{Error, Octocrab};
+use strsim::levenshtein;
 use tracing::log;
 
 use crate::bors::event::PullRequestComment;
@@ -287,6 +288,72 @@ impl GithubRepositoryClient {
         run_ids.map(|workflow_id| self.get_workflow_url(workflow_id))
     }
 
+    /// Validates a reviewer's GitHub username and returns validation results if the username is invalid.
+    /// If multiple reviewers are provided (comma-separated), validates each one.
+    /// Returns a validation result for the first invalid username encountered, or None if all usernames are valid.
+    pub async fn validate_reviewers(&self, reviewer_list: &str) -> anyhow::Result<Option<Comment>> {
+        if reviewer_list.trim().is_empty() {
+            return Ok(Some(Comment::new(
+                "Error: No reviewer specified. Use r=username to specify a reviewer.".to_string(),
+            )));
+        }
+
+        for username in reviewer_list.split(',').map(|s| s.trim()) {
+            if username.is_empty() {
+                return Ok(Some(Comment::new(
+                    "Error: Empty reviewer name provided. Use r=username to specify a reviewer."
+                        .to_string(),
+                )));
+            }
+
+            match self.client.users(username).profile().await {
+                Ok(_) => continue, // user exist continue
+                Err(octocrab::Error::GitHub { source, .. }) => {
+                    if source.message.contains("Not Found") {
+                        let similar_usernames = self.find_similar_usernames(username).await?;
+
+                        let mut message = format!("Invalid reviewer username: `{}`", username);
+                        if !similar_usernames.is_empty() {
+                            message.push_str("\nDid you mean one of these users?\n");
+                            for similar in similar_usernames {
+                                message.push_str(&format!("- {}\n", similar));
+                            }
+                        }
+
+                        return Ok(Some(Comment::new(message)));
+                    }
+                }
+                Err(_) => continue,
+            }
+        }
+        Ok(None)
+    }
+
+    /// Searches for GitHub usernames similar to the provided username using Levenshtein distance.
+    async fn find_similar_usernames(&self, username: &str) -> anyhow::Result<Vec<String>> {
+        const MAX_DISTANCE: usize = 2;
+
+        let search_results = self
+            .client
+            .search()
+            .users(username)
+            .send()
+            .await
+            .context("Failed to search for similar usernames")?;
+
+        let similar_usernames = search_results
+            .items
+            .into_iter()
+            .filter(|user| {
+                let distance = levenshtein(username, &user.login);
+                distance > 0 && distance <= MAX_DISTANCE
+            })
+            .map(|user| user.login)
+            .collect();
+
+        Ok(similar_usernames)
+    }
+
     fn format_pr(&self, pr: PullRequestNumber) -> String {
         format!("{}/{}", self.repository(), pr)
     }