diff --git a/asm/assemble.c b/asm/assemble.c
index 7a832322..321f9659 100644
--- a/asm/assemble.c
+++ b/asm/assemble.c
@@ -2343,7 +2343,7 @@ static inline void emit_rex(struct out_data *data, insn *ins)
         } else if (rex & REX_P) {
             buf[n++] = rex;
         } else {
-            nasm_assert(!rex);
+            nasm_assert(!(rex & ~REX_L));
         }
 
         if (ins->vex_cm) {
diff --git a/x86/insns.dat b/x86/insns.dat
index a0f2e33a..219e3269 100644
--- a/x86/insns.dat
+++ b/x86/insns.dat
@@ -469,10 +469,14 @@ $dq   RDPID	reg#				[m:	f3 !osp o# 0f c7 /7]			RDPID
       SMSW	reg64				[m:	o64nw 0f 01 /4]				X86_64,LONG,ND
 $wdq  SMSW	reg#				[m:	o# 0f 01 /4]				286
 
-$dq   MOV	reg#,reg_creg			[mr:	nw w# rex.l 0f 20 /r]			386,PRIV
-$dq   MOV	reg_creg,reg#			[rm:	nw w# rex.l 0f 22 /r]			386,PRIV
-$dq   MOV	reg#,reg_dreg			[mr:	nw w# 0f 21 /r]				386,PRIV
-$dq   MOV	reg_dreg,reg#			[rm:	nw w# 0f 23 /r]				386,PRIV,NOLONG
+      MOV	reg32,reg_creg			[mr:	rex.l 0f 20 /r]				386,NOLONG,PRIV
+      MOV	reg_creg,reg32			[rm:	rex.l 0f 22 /r]				386,NOLONG,PRIV
+      MOV	reg64,reg_creg			[mr:	o64nw 0f 20 /r]				X86_64,LONG,PRIV
+      MOV	reg_creg,reg64			[rm:	o64nw 0f 22 /r]				X86_64,LONG,PRIV
+      MOV	reg32,reg_dreg			[mr:	0f 21 /r]				386,NOLONG,PRIV
+      MOV	reg_dreg,reg32			[rm:	0f 23 /r]				386,NOLONG,PRIV
+      MOV	reg64,reg_dreg			[mr:	o64nw 0f 21 /r]				X86_64,LONG,PRIV
+      MOV	reg_dreg,reg64			[rm:	o64nw 0f 23 /r]				X86_64,LONG,PRIV
       MOV	reg32,reg_treg			[mr:	0f 24 /r]				386,NOLONG,ND,OBSOLETE
       MOV	reg_treg,reg32			[rm:	0f 26 /r]				386,NOLONG,ND,OBSOLETE
 
diff --git a/x86/preinsns.pl b/x86/preinsns.pl
index 16b9465c..992eb973 100755
--- a/x86/preinsns.pl
+++ b/x86/preinsns.pl
@@ -204,7 +204,9 @@ sub func_multisize($$$) {
 	$o .= ',NOLONG' if ($long & 2);
 	$o .= ',ND'     if ($nd);
 
-	$o .= ',386'    if ($s >= 32 && $o !~ /\B\!386\b/);
+	if ($s >= 32 && $o !~ /\B\!386\b/ && $o =~ /\b(8086|[12]86)\b/) {
+	    $o .= ',386';
+	}
 
 	push(@ol, $o);
     }
@@ -499,10 +501,9 @@ sub adjust_instruction_flags(@) {
 	return undef;
     }
 
-    if ($i[2] =~ /\ba16\b/) {
+    if ($i[2] =~ /\b(a16|rex\.l)\b/) {
 	add_flag($i[3], 'NOLONG');
-    }
-    if ($i[2] =~ /\b(o64(nw)?\b|rex2?|a64\b)/) {
+    } elsif ($i[2] =~ /\b(o64(nw)?\b|rex2?|a64\b)/) {
 	add_flag($i[3], 'LONG');
     }
     if (has_flag($i[3], 'NOLONG') && has_flag($i[3], 'LONG')) {