diff --git a/src/devices/machine/hd63450.cpp b/src/devices/machine/hd63450.cpp
index 85cf00bfa86..cd2906aa583 100644
--- a/src/devices/machine/hd63450.cpp
+++ b/src/devices/machine/hd63450.cpp
@@ -93,7 +93,7 @@ void hd63450_device::device_reset()
 		m_reg[x].ocr = 0;
 		m_reg[x].scr = 0;
 		m_reg[x].ccr = 0;
-		m_reg[x].csr &= 0xfe;
+		m_reg[x].csr &= 0x01;
 		m_reg[x].cer = 0;
 		m_reg[x].gcr = 0;