diff --git a/am29f040b.c b/am29f040b.c
index ae345e5..9d770cf 100644
--- a/am29f040b.c
+++ b/am29f040b.c
@@ -92,7 +92,7 @@
 
 int erase_29f040b (struct flashchip * flash)
 {
-	volatile char * bios = flash->virt_addr;
+	volatile unsigned char * bios = flash->virt_addr;
 
 	*(bios + 0x555) = 0xAA;
 	*(bios + 0x2AA) = 0x55;