diff --git a/Source/HBIOS/Config/RC_ez80.asm b/Source/HBIOS/Config/RC_ez80.asm
index 057a5547..895b9075 100644
--- a/Source/HBIOS/Config/RC_ez80.asm
+++ b/Source/HBIOS/Config/RC_ez80.asm
@@ -6,6 +6,7 @@
 #include "cfg_rc.asm"
 ;
 CPUOSC		.SET	10000000	; CPU OSC FREQ
+DEFSIOCLK	.SET	1843200		; SIO CLOCK FREQ
 DEFSERCFG	.SET	SER_115200_8N1	; DEFAULT SERIAL LINE CONFIG (SHOULD MATCH ABOVE)
 ;
 SIOENABLE	.SET	TRUE		; TRUE TO AUTO-DETECT ZILOG SIO/2