diff --git a/src/js/internal/sql/mysql.ts b/src/js/internal/sql/mysql.ts
index 187efe17d0e..a145b3d07df 100644
--- a/src/js/internal/sql/mysql.ts
+++ b/src/js/internal/sql/mysql.ts
@@ -20,6 +20,8 @@ const {
   init: initMySQL,
 } = $zig("mysql.zig", "createBinding") as MySQLDotZig;
 
+const upsertSuffixRegExp = /\bON\s+DUPLICATE\s+KEY\s+UPDATE\s*$/i;
+
 function wrapError(error: Error | MySQLErrorOptions) {
   if (Error.isError(error)) {
     return error;
@@ -280,7 +282,9 @@ class MySQLAdapter
   }
 
   isUpsertUpdate(query: string): boolean {
-    return query.trimEnd().endsWith("ON DUPLICATE KEY UPDATE");
+    // SQL keywords are case-insensitive and separated by arbitrary whitespace,
+    // so accept any spelling of the clause
+    return upsertSuffixRegExp.test(query);
   }
 }
 
diff --git a/test/js/sql/sql-mysql-upsert-keyword-case.test.ts b/test/js/sql/sql-mysql-upsert-keyword-case.test.ts
new file mode 100644
index 00000000000..adfe0e17f50
--- /dev/null
+++ b/test/js/sql/sql-mysql-upsert-keyword-case.test.ts
@@ -0,0 +1,163 @@
+// The MySQL helper normalizer appends " SET " after an update helper unless the
+// query already ends with ON DUPLICATE KEY UPDATE. SQL keywords are
+// case-insensitive and separated by arbitrary whitespace, so the suffix check
+// must accept any spelling; a lowercase one used to produce
+// "... on duplicate key update SET `age` = ?", which is invalid.
+// https://github.com/oven-sh/bun/issues/32035
+//
+// Uses a minimal mock MySQL server that captures the text of every
+// COM_STMT_PREPARE and replies with an error packet, so the test can assert
+// the exact generated SQL without Docker.
+
+import { SQL } from "bun";
+import { expect, test } from "bun:test";
+import { once } from "events";
+import net from "net";
+
+function u16le(n: number) {
+  return Buffer.from([n & 0xff, (n >> 8) & 0xff]);
+}
+function u24le(n: number) {
+  return Buffer.from([n & 0xff, (n >> 8) & 0xff, (n >> 16) & 0xff]);
+}
+function u32le(n: number) {
+  return Buffer.from([n & 0xff, (n >> 8) & 0xff, (n >> 16) & 0xff, (n >>> 24) & 0xff]);
+}
+function packet(seq: number, payload: Buffer) {
+  return Buffer.concat([u24le(payload.length), Buffer.from([seq]), payload]);
+}
+
+// Server capability flags (subset sufficient for the prepared-statement path).
+const CLIENT_PROTOCOL_41 = 1 << 9;
+const CLIENT_SECURE_CONNECTION = 1 << 15;
+const CLIENT_PLUGIN_AUTH = 1 << 19;
+const CLIENT_PLUGIN_AUTH_LENENC_CLIENT_DATA = 1 << 21;
+const CLIENT_DEPRECATE_EOF = 1 << 24;
+const SERVER_CAPS =
+  CLIENT_PROTOCOL_41 |
+  CLIENT_SECURE_CONNECTION |
+  CLIENT_PLUGIN_AUTH |
+  CLIENT_PLUGIN_AUTH_LENENC_CLIENT_DATA |
+  CLIENT_DEPRECATE_EOF;
+
+function handshakeV10() {
+  const authData1 = Buffer.alloc(8, 0x61);
+  const authData2 = Buffer.alloc(13, 0x62); // includes trailing NUL as part of 13 bytes
+  authData2[12] = 0;
+  const payload = Buffer.concat([
+    Buffer.from([10]), // protocol version
+    Buffer.from("mock-5.7.0\0"), // server version NUL-terminated
+    u32le(1), // connection id
+    authData1, // auth-plugin-data-part-1 (8)
+    Buffer.from([0]), // filler
+    u16le(SERVER_CAPS & 0xffff), // capability flags lower
+    Buffer.from([0x2d]), // character set (utf8mb4_general_ci)
+    u16le(0x0002), // status flags (SERVER_STATUS_AUTOCOMMIT)
+    u16le((SERVER_CAPS >>> 16) & 0xffff), // capability flags upper
+    Buffer.from([21]), // length of auth-plugin-data
+    Buffer.alloc(10, 0), // reserved
+    authData2, // auth-plugin-data-part-2 (13 bytes)
+    Buffer.from("mysql_native_password\0"),
+  ]);
+  return packet(0, payload);
+}
+
+function okPacket(seq: number) {
+  // header, affected_rows (lenenc 0), last_insert_id (lenenc 0), status flags, warnings
+  return packet(seq, Buffer.from([0x00, 0x00, 0x00, 0x02, 0x00, 0x00, 0x00]));
+}
+
+function errorPacket(seq: number, errno: number, message: string) {
+  const payload = Buffer.concat([Buffer.from([0xff]), u16le(errno), Buffer.from("#42000"), Buffer.from(message)]);
+  return packet(seq, payload);
+}
+
+const COM_QUERY = 0x03;
+const COM_STMT_PREPARE = 0x16;
+
+test("upsert helper omits SET for every spelling of ON DUPLICATE KEY UPDATE", async () => {
+  const prepared: string[] = [];
+
+  const server = net.createServer(socket => {
+    let buffered = Buffer.alloc(0);
+    let authed = false;
+
+    socket.write(handshakeV10());
+
+    socket.on("data", chunk => {
+      buffered = Buffer.concat([buffered, chunk]);
+      while (buffered.length >= 4) {
+        const len = buffered[0] | (buffered[1] << 8) | (buffered[2] << 16);
+        if (buffered.length < 4 + len) break;
+        const seq = buffered[3];
+        const payload = buffered.subarray(4, 4 + len);
+        buffered = buffered.subarray(4 + len);
+
+        if (!authed) {
+          // HandshakeResponse41 from client → accept unconditionally.
+          authed = true;
+          socket.write(okPacket(seq + 1));
+          continue;
+        }
+
+        const cmd = payload[0];
+        if (cmd === COM_STMT_PREPARE) {
+          // Capture the normalized query text, then fail the statement; the
+          // assertion below is on the generated SQL, not on execution.
+          prepared.push(payload.subarray(1).toString("utf-8"));
+          socket.write(errorPacket(seq + 1, 1064, "mock: rejecting every prepare"));
+        } else if (cmd === COM_QUERY) {
+          socket.write(okPacket(seq + 1));
+        } else {
+          // COM_QUIT or anything else → close.
+          socket.end();
+        }
+      }
+    });
+  });
+
+  server.listen(0, "127.0.0.1");
+  await once(server, "listening");
+  const { port } = server.address() as net.AddressInfo;
+
+  try {
+    await using sql = new SQL({ url: `mysql://root@127.0.0.1:${port}/db`, max: 1 });
+
+    const row = { id: 1, age: 30 };
+    const update = { age: 31 };
+
+    // Same upsert with four spellings of the clause (case and whitespace are
+    // both flexible in SQL); each must reach the server (errno 1064 proves the
+    // round-trip happened).
+    const errUpper = await sql`INSERT INTO users ${sql(row)} ON DUPLICATE KEY UPDATE ${sql(update)}`.catch(
+      (e: any) => e,
+    );
+    expect(errUpper?.errno).toBe(1064);
+
+    const errLower = await sql`INSERT INTO users ${sql(row)} on duplicate key update ${sql(update)}`.catch(
+      (e: any) => e,
+    );
+    expect(errLower?.errno).toBe(1064);
+
+    const errMixed = await sql`INSERT INTO users ${sql(row)} On Duplicate Key Update ${sql(update)}`.catch(
+      (e: any) => e,
+    );
+    expect(errMixed?.errno).toBe(1064);
+
+    const errWhitespace = await sql`INSERT INTO users ${sql(row)} on\n  Duplicate\tKEY   update ${sql(update)}`.catch(
+      (e: any) => e,
+    );
+    expect(errWhitespace?.errno).toBe(1064);
+
+    // No "SET" after the keyword in any spelling; the update helper's columns
+    // follow it directly.
+    expect(prepared).toEqual([
+      "INSERT INTO users (`id`, `age`) VALUES(?, ?)  ON DUPLICATE KEY UPDATE `age` = ? ",
+      "INSERT INTO users (`id`, `age`) VALUES(?, ?)  on duplicate key update `age` = ? ",
+      "INSERT INTO users (`id`, `age`) VALUES(?, ?)  On Duplicate Key Update `age` = ? ",
+      "INSERT INTO users (`id`, `age`) VALUES(?, ?)  on\n  Duplicate\tKEY   update `age` = ? ",
+    ]);
+  } finally {
+    await new Promise<void>(r => server.close(() => r()));
+  }
+});
diff --git a/test/js/sql/sql-mysql.helpers.test.ts b/test/js/sql/sql-mysql.helpers.test.ts
index be599c02a0c..92d9de9dcfd 100644
--- a/test/js/sql/sql-mysql.helpers.test.ts
+++ b/test/js/sql/sql-mysql.helpers.test.ts
@@ -225,6 +225,54 @@ describeWithContainer(
         expect(result[0].email).toBe("bunny2@bun.com");
       }
     });
+
+    // SQL keywords are case-insensitive; lowercase spellings must not get an
+    // extra SET appended. https://github.com/oven-sh/bun/issues/32035
+    test("upsert helper with lowercase on duplicate key update", async () => {
+      await using sql = new SQL({ ...getOptions(), max: 1 });
+      const random_name = "test_" + randomUUIDv7("hex").replaceAll("-", "");
+      await sql`
+      CREATE TABLE IF NOT EXISTS ${sql(random_name)} (
+          id int PRIMARY KEY,
+          foo text NOT NULL,
+          email VARCHAR(255) NOT NULL UNIQUE
+      )
+    `;
+
+      await sql`INSERT INTO ${sql(random_name)} ${sql({ id: 1, foo: "hello", email: "bunny@bun.com" })}`;
+
+      {
+        const data = { foo: "hello2", email: "bunny2@bun.com" };
+        await sql`
+      INSERT INTO ${sql(random_name)} ${sql({ id: 1, ...data })}
+      on duplicate key update ${sql(data)}
+    `;
+        const result = await sql`SELECT * FROM ${sql(random_name)}`;
+        expect(result).toEqual([{ id: 1, foo: "hello2", email: "bunny2@bun.com" }]);
+      }
+
+      {
+        const data = { foo: "hello3", email: "bunny3@bun.com" };
+        await sql`
+      INSERT INTO ${sql(random_name)} ${sql({ id: 1, ...data })}
+      On Duplicate Key Update ${sql(data)}
+    `;
+        const result = await sql`SELECT * FROM ${sql(random_name)}`;
+        expect(result).toEqual([{ id: 1, foo: "hello3", email: "bunny3@bun.com" }]);
+      }
+
+      // keyword whitespace is flexible too
+      {
+        const data = { foo: "hello4", email: "bunny4@bun.com" };
+        await sql`
+      INSERT INTO ${sql(random_name)} ${sql({ id: 1, ...data })}
+      on duplicate key
+      UPDATE ${sql(data)}
+    `;
+        const result = await sql`SELECT * FROM ${sql(random_name)}`;
+        expect(result).toEqual([{ id: 1, foo: "hello4", email: "bunny4@bun.com" }]);
+      }
+    });
     test("update helper with IN and column name", async () => {
       await using sql = new SQL({ ...getOptions(), max: 1 });
       const random_name = "test_" + randomUUIDv7("hex").replaceAll("-", "");