diff --git a/internal/pmtud/tcp/tcp.go b/internal/pmtud/tcp/tcp.go
index 79decfb9..ad9e544e 100644
--- a/internal/pmtud/tcp/tcp.go
+++ b/internal/pmtud/tcp/tcp.go
@@ -103,19 +103,12 @@ func runTest(ctx context.Context, fd fileDescriptor,
 		return fmt.Errorf("%w: expected %d, got %d", errTCPSynAckAckMismatch, synSeq+1, synAckAck)
 	}
 
-	// Send a no-data ACK packet to finish the 3-way handshake.
-	const ackMTU = 0 // no data payload initially
-	ackPacket := createACKPacket(src, dst, synAckAck, synAckSeq+1, ackMTU)
+	// Send an ACK packet to finish the 3-way handshake, together with the
+	// data to test the MTU, using TCP fast-open.
+	ackPacket := createACKPacket(src, dst, synAckAck, synAckSeq+1, mtu)
 	err = sendTo(fd, ackPacket, sendToFlags, dstSockAddr)
 	if err != nil {
-		return fmt.Errorf("sending ACK-without-data packet: %w", err)
-	}
-
-	// Send a data ACK packet to test the MTU given.
-	ackPacket = createACKPacket(src, dst, synAckAck, synAckSeq+1, mtu)
-	err = sendTo(fd, ackPacket, sendToFlags, dstSockAddr)
-	if err != nil {
-		return fmt.Errorf("sending ACK-with-data packet: %w", err)
+		return fmt.Errorf("sending ACK packet: %w", err)
 	}
 
 	select {