diff --git a/kernel/iec_listener.c b/kernel/iec_listener.c
index 3d73d4b..7e25d49 100644
--- a/kernel/iec_listener.c
+++ b/kernel/iec_listener.c
@@ -242,7 +242,16 @@ static enum iec_rx receive_byte(u8 *out, bool *eoi, bool data_phase)
 			value |= (1u << i);
 	}
 
-	/* 4. BYTE ACKNOWLEDGE: pull DATA low (Tf), hold for the next RFD */
+	/* 4. BYTE ACKNOWLEDGE: wait for the talker to pull CLK low at end of
+	 *    byte (mirrors the reference listener), THEN pull DATA low (Tf).
+	 *    Without this wait we would assert the ack while CLK is still high
+	 *    from bit 7, racing the talker's end-of-byte edge and desyncing the
+	 *    handshake. The next receive_byte() releases DATA after CLK goes high
+	 *    again (RFD), completing the per-byte handshake. */
+	rc = wait_clk(true /* asserted: talker finished the byte */,
+		      IEC_CLK_TIMEOUT_US, data_phase);
+	if (rc != IEC_RX_OK)
+		goto out;
 	iec_data_assert();
 	*out = value;
 	rc = IEC_RX_OK;