diff --git a/decode_arm.s b/decode_arm.s
index a5a1ce0..5b5e013 100644
--- a/decode_arm.s
+++ b/decode_arm.s
@@ -109,13 +109,13 @@ copyLiteralFinish:
 	MOVB.NE   tmp2, -1(dst)
 
 copyLiteralDone:
-	CMP src, srcend
-	BEQ end
-
 	// Initial part of match length.
 	// This frees up the token register for reuse as offset.
 	AND $15, token, len
 
+	CMP src, srcend
+	BEQ end
+
 	// Read offset.
 	ADD.S $2, src
 	BCS   shortSrc
@@ -188,6 +188,8 @@ copyMatchDone:
 	BNE loop
 
 end:
+	CMP  $0, len
+	BNE  corrupt
 	SUB  dstorig, dst, tmp1
 	MOVW tmp1, ret+24(FP)
 	RET
diff --git a/decode_arm64.s b/decode_arm64.s
index aa73a1c..abc306b 100644
--- a/decode_arm64.s
+++ b/decode_arm64.s
@@ -112,6 +112,9 @@ copyLiteralShortEnd:
 	MOVB.P  tmp4, 1(dst)
 
 copyLiteralDone:
+	// Initial part of match length.
+	AND $15, token, len
+
 	CMP src, srcend
 	BEQ end
 
@@ -123,8 +126,7 @@ copyLiteralDone:
 	MOVHU -2(src), offset
 	CBZ   offset, corrupt
 
-	// Read match length.
-	AND $15, token, len
+	// Read rest of match length.
 	CMP $15, len
 	BNE readMatchlenDone
 
@@ -163,29 +165,30 @@ copyMatchTry8:
 	AND    $7, len, lenRem
 	SUB    $8, len
 copyMatchLoop8:
-	SUBS   $8, len
 	MOVD.P 8(match), tmp1
 	MOVD.P tmp1, 8(dst)
+	SUBS   $8, len
 	BPL    copyMatchLoop8
 
-	ADD  lenRem, match
+	MOVD (match)(len), tmp2 // match+len == match+lenRem-8.
 	ADD  lenRem, dst
-	MOVD -8(match), tmp2
+	MOVD $0, len
 	MOVD tmp2, -8(dst)
 	B    copyMatchDone
 
 copyMatchLoop1:
-	// Finish with a byte-at-a-time copy.
-	SUB     $1, len
+	// Byte-at-a-time copy for small offsets.
 	MOVBU.P 1(match), tmp2
 	MOVB.P  tmp2, 1(dst)
-	CBNZ    len, copyMatchLoop1
+	SUBS    $1, len
+	BNE     copyMatchLoop1
 
 copyMatchDone:
 	CMP src, srcend
 	BNE loop
 
 end:
+	CBNZ len, corrupt
 	SUB  dstorig, dst, tmp1
 	MOVD tmp1, ret+48(FP)
 	RET
diff --git a/decode_asm.go b/decode_asm.go
index eb05ace..4f0bb37 100644
--- a/decode_asm.go
+++ b/decode_asm.go
@@ -1,3 +1,4 @@
+//go:build (amd64 || arm || arm64) && !appengine && gc && !noasm
 // +build amd64 arm arm64
 // +build !appengine
 // +build gc