diff --git a/libsrc/cbm/oserror.s b/libsrc/cbm/oserror.s
index 3fa7b3e1e..1f40685cb 100644
--- a/libsrc/cbm/oserror.s
+++ b/libsrc/cbm/oserror.s
@@ -18,10 +18,10 @@ __osmaperrno:
     	dex
     	bne	@L1	        ; Next entry
 
-; Code not found, return EINVAL
+; Code not found, return EUNKNOWN
 
-	lda	#<EINVAL
-	ldx	#>EINVAL
+	lda	#<EUNKNOWN
+	ldx	#>EUNKNOWN
 	rts
 
 ; Found the code