diff --git a/src/memtest.s b/src/memtest.s
index beb7e54..120a60b 100644
--- a/src/memtest.s
+++ b/src/memtest.s
@@ -18,7 +18,7 @@
 ; RAM testing routine. Ported to 6809 from 6800, based on source for ROBIT-2 for
 ; MIKBUG.
 RAMTEST
-  ldx #SRAM_BASE
+  ldx #STACK_TOP+1     ; bottom of testable SRAM, $0200
 AGAIN@                 ; Store 1 in memory
   lda #1               ; Set [X] to 1
   sta 0,x