diff --git a/mps/src/sso1al.s b/mps/src/sso1al.s
new file mode 100644
index 00000000000..e9594764c73
--- /dev/null
+++ b/mps/src/sso1al.s
@@ -0,0 +1,42 @@
+ # impl.s.sso1al: STACK SCANNING FOR DIGITAL UNIX / ALPHA
+ #
+ # $HopeName$
+ # Copyright (C) 1997 Harlequin Group, all rights reserved
+ #
+ # .readership: Any MPS developer that is prepared to read Alpha
+ # assembly code in DIGITAL UNIX 'as' syntax.
+ #
+ # See design.mps.sso1al for the design.
+
+
+.globl	StackScan
+.globl	TraceScanAreaTagged
+
+.ent	StackScan
+StackScan:
+ldgp	$gp,0($27)	# faff with global pointer
+lda	$sp,-64($sp)	# build and declare frame and saveregs
+.frame	$sp,64,$26
+.mask	0x400FE00,-64
+stq	$26,0($sp)	# dump ra and other regs so that they get fixed
+stq	$9,8($sp)
+stq	$10,16($sp)
+stq	$11,24($sp)
+stq	$12,32($sp)
+stq	$13,40($sp)
+stq	$14,48($sp)
+stq	$15,56($sp)
+.prologue	1
+
+ # bis $31,$16,$16 1st arg to TraceScanAreaTagged is same as our 1st arg
+bis	$31,$17,$18	# area to be scanned is from $sp to StackBot
+bis	$31,$sp,$17
+
+jsr	$26,TraceScanAreaTagged
+ldgp	$gp,0($26)
+ # our result is TraceScanAreaTagged's result, so leave $0 untouched
+
+ldq	$26,0($sp)
+lda	$sp,+64($sp)
+ret	$31,($26),1
+.end	StackScan