diff --git a/crypto/perlasm/x86gas.pl b/crypto/perlasm/x86gas.pl
index 99d7c1b..55d09d8 100644
--- a/crypto/perlasm/x86gas.pl
+++ b/crypto/perlasm/x86gas.pl
@@ -17,7 +17,7 @@
 { my $reg=shift;
     if    ($reg =~ m/^%e/o)		{ "l"; }
     elsif ($reg =~ m/^%[a-d][hl]$/o)	{ "b"; }
-    elsif ($reg =~ m/^%[xm]/o)		{ undef; }
+    elsif ($reg =~ m/^%[yxm]/o)		{ undef; }
     else				{ "w"; }
 }