diff --git a/libsrc/gamate/joy/gamate-stdjoy.s b/libsrc/gamate/joy/gamate-stdjoy.s
index a5bd24ef2..801b40acd 100644
--- a/libsrc/gamate/joy/gamate-stdjoy.s
+++ b/libsrc/gamate/joy/gamate-stdjoy.s
@@ -79,7 +79,7 @@ COUNT:
 
 READJOY:
         lda     JOY_DATA
-        eor     #$ff
+        eor     #$FF
         ldx     #0
         rts