diff --git a/presets/zx/bios.c b/presets/zx/bios.c
index 155db723..db42198c 100644
--- a/presets/zx/bios.c
+++ b/presets/zx/bios.c
@@ -17,6 +17,7 @@ int putchar(int ch) {
     ld	a,4 (ix)
     rst 0x10
   __endasm;
+  return ch;
 }
 
 void beep(int divisor, int duration) {