diff --git a/quotesdb/src/bin/api/db/d1.rs b/quotesdb/src/bin/api/db/d1.rs
index 65dc6f3..16fb233 100644
--- a/quotesdb/src/bin/api/db/d1.rs
+++ b/quotesdb/src/bin/api/db/d1.rs
@@ -569,32 +569,45 @@ impl QuoteRepository for D1Repository {
     /// Replace the admin auth code if `current` matches the stored value.
     ///
     /// Generates a fresh 4-word passphrase when `new_code` is `None`.
-    /// Returns `Err(DbError::Forbidden)` if `current` does not match the stored code.
+    ///
+    /// The check and update are performed atomically via a single
+    /// `UPDATE … WHERE key = 'admin_auth_code' AND value = ?current` statement.
+    /// The result metadata's `changes` count is inspected: if zero rows were
+    /// affected the stored code either does not exist or did not match `current`,
+    /// and `Err(DbError::Forbidden)` is returned. If one row was affected the new
+    /// code is returned.
     async fn update_admin_auth_code(
         &self,
         current: &str,
         new_code: Option<&str>,
     ) -> Result<String, DbError> {
-        let stored = self.get_admin_auth_code().await?;
-        if stored.as_deref() != Some(current) {
-            return Err(DbError::Forbidden);
-        }
-
         let replacement = new_code
             .map(|s| s.to_owned())
             .unwrap_or_else(generate_auth_code);
 
-        self.db
+        let result = self
+            .db
             .prepare(
-                "INSERT INTO admin_config (key, value) VALUES ('admin_auth_code', ?1) \
-                 ON CONFLICT(key) DO UPDATE SET value = excluded.value",
+                "UPDATE admin_config \
+                 SET value = ?1 \
+                 WHERE key = 'admin_auth_code' AND value = ?2",
             )
-            .bind(&[JsValue::from_str(&replacement)])
+            .bind(&[JsValue::from_str(&replacement), JsValue::from_str(current)])
             .map_err(|e| DbError::Internal(e.to_string()))?
             .run()
             .await
             .map_err(|e| DbError::Internal(e.to_string()))?;
 
+        let changes = result
+            .meta()
+            .map_err(|e| DbError::Internal(e.to_string()))?
+            .and_then(|m| m.changes)
+            .unwrap_or(0);
+
+        if changes == 0 {
+            return Err(DbError::Forbidden);
+        }
+
         Ok(replacement)
     }
 
diff --git a/quotesdb/src/bin/api/db/native.rs b/quotesdb/src/bin/api/db/native.rs
index 14b0008..573d6f0 100644
--- a/quotesdb/src/bin/api/db/native.rs
+++ b/quotesdb/src/bin/api/db/native.rs
@@ -513,34 +513,40 @@ impl QuoteRepository for NativeRepository {
     /// Replace the admin auth code if `current` matches the stored value.
     ///
     /// Generates a fresh 4-word passphrase when `new_code` is `None`.
-    /// Returns `Err(DbError::Forbidden)` if `current` does not match the stored code.
+    ///
+    /// The check and update are performed atomically via a single
+    /// `UPDATE … WHERE key = 'admin_auth_code' AND value = ?current` statement.
+    /// If zero rows are affected the stored code either does not exist or did not
+    /// match `current`, and `Err(DbError::Forbidden)` is returned. If one row is
+    /// affected the new code is returned.
     async fn update_admin_auth_code(
         &self,
         current: &str,
         new_code: Option<&str>,
     ) -> Result<String, DbError> {
-        let stored = self.get_admin_auth_code().await?;
-        if stored.as_deref() != Some(current) {
-            return Err(DbError::Forbidden);
-        }
-
         let replacement = new_code
             .map(|s| s.to_owned())
             .unwrap_or_else(generate_auth_code);
-        let replacement2 = replacement.clone();
+        let current = current.to_owned();
+        let replacement_inner = replacement.clone();
 
-        self.conn
+        let changed = self
+            .conn
             .call(move |conn| {
-                conn.execute(
-                    "INSERT INTO admin_config (key, value) VALUES ('admin_auth_code', ?1) \
-                     ON CONFLICT(key) DO UPDATE SET value = excluded.value",
-                    rusqlite::params![replacement2],
-                )?;
-                Ok(())
+                Ok(conn.execute(
+                    "UPDATE admin_config \
+                     SET value = ?1 \
+                     WHERE key = 'admin_auth_code' AND value = ?2",
+                    rusqlite::params![replacement_inner, current],
+                )?)
             })
             .await
             .map_err(|e| DbError::Internal(e.to_string()))?;
 
+        if changed == 0 {
+            return Err(DbError::Forbidden);
+        }
+
         Ok(replacement)
     }
 
diff --git a/quotesdb/src/bin/api/handlers/mod.rs b/quotesdb/src/bin/api/handlers/mod.rs
index 91088f5..33f37e8 100644
--- a/quotesdb/src/bin/api/handlers/mod.rs
+++ b/quotesdb/src/bin/api/handlers/mod.rs
@@ -510,9 +510,12 @@ struct ResetAuthCodeResponse {
 /// { "auth_code": "word-word-word-word" }
 /// ```
 ///
-/// Returns `403 Forbidden` if the header is absent or the code is incorrect.
-/// The DB layer (`update_admin_auth_code`) performs the auth check internally
-/// and returns `DbError::Forbidden` on mismatch.
+/// Returns `403 Forbidden` in two cases:
+/// - Missing `X-Admin-Code` header — the handler returns `403` immediately,
+///   before any database call.
+/// - Wrong code — the DB layer (`update_admin_auth_code`) returns
+///   `DbError::Forbidden` when the supplied code does not match the stored
+///   value, which the handler maps to `403`.
 #[cfg_attr(target_arch = "wasm32", worker::send)]
 async fn reset_auth_code(
     State(repo): State<Repo>,