diff --git a/src/main.rs b/src/main.rs
index 8a5c6d2..cdf82fe 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -50,7 +50,7 @@ struct MinimalMemberWithoutId {
 }
 
 #[derive(Responder)]
-#[response(status = 500, content_type = "json")]
+#[response(status = 500, content_type = "text/plain")]
 struct ErrorResponder {
     message: String
 }
@@ -81,6 +81,21 @@ async fn add_member(db: &State<DatabaseConnection>, minimalMemberWithoutId: Json
     // Grab the database connection
     let db = db as &DatabaseConnection;
 
+    // Check if a member with the same NTNU username already exists
+    let matching_member: Option<members::Model> = Members::find() // Find a member in the "Members" table
+        .filter(members::Column::NtnuUsername.eq(minimalMemberWithoutId.ntnuUsername.to_owned())) // Filter by the provided username in the NtnuUsername column
+        .one(db) // We only care about one result
+        .await?; // Wait for the result
+
+    // If a member exists return an error
+    if matching_member.is_some() {
+        return Err(
+            ErrorResponder {
+                message: "A member with this NTNU username already exists".to_string(),
+            }
+        )
+    }
+
     // Create the new member info from the provided JSON
     let new_member = members::ActiveModel {
         ntnu_username: ActiveValue::Set(minimalMemberWithoutId.ntnuUsername.to_owned()),
@@ -108,6 +123,7 @@ async fn add_member(db: &State<DatabaseConnection>, minimalMemberWithoutId: Json
         },
     }
 
+    // Put the fetched info into a minimal member for returning
     let member = MinimalMember {
         id: new_member.id,
         ntnuUsername: new_member.ntnu_username,