diff --git a/rdisk.h b/rdisk.h
index a9ed1c6..1b43ea8 100644
--- a/rdisk.h
+++ b/rdisk.h
@@ -14,8 +14,8 @@ OSErr RDiskReadXPRAM(short numBytes, short whichByte, Ptr dest) = {0x4840, 0x300
 #pragma parameter __D0 RDiskAddDrive(__D1, __D0, __A0)
 OSErr RDiskAddDrive(short drvrRefNum, short drvNum, DrvQElPtr dq) = {0x4840, 0x3001, 0xA04E};
 
-static inline char RDiskIsRPressed() { return *((char*)0x175) & 0x80; }
-static inline char RDiskIsAPressed() { return *((char*)0x174) & 0x01; }
+static inline char RDiskIsRPressed() { return *((volatile char*)0x175) & 0x80; }
+static inline char RDiskIsAPressed() { return *((volatile char*)0x174) & 0x01; }
 
 //#define RDISK_COMPRESS_ICON_ENABLE
 #define RDISK_ICON_SIZE (285)