diff --git a/basis/cpu/x86/assembler/assembler-tests.factor b/basis/cpu/x86/assembler/assembler-tests.factor
index 941bbe5b73..915847a453 100644
--- a/basis/cpu/x86/assembler/assembler-tests.factor
+++ b/basis/cpu/x86/assembler/assembler-tests.factor
@@ -4,9 +4,9 @@ IN: cpu.x86.assembler.tests
 [ { HEX: 49 HEX: 89 HEX: 04 HEX: 24 } ] [ [ R12 [] RAX MOV ] { } make ] unit-test
 [ { HEX: 49 HEX: 8b HEX: 06 } ] [ [ RAX R14 [] MOV ] { } make ] unit-test
 
-! [ { HEX: 89 HEX: ca } ] [ [ EDX ECX MOV ] { } make ] unit-test
-! [ { HEX: 4c HEX: 89 HEX: e2 } ] [ [ RDX R12 MOV ] { } make ] unit-test
-! [ { HEX: 49 HEX: 89 HEX: d4 } ] [ [ R12 RDX MOV ] { } make ] unit-test
+[ { HEX: 89 HEX: ca } ] [ [ EDX ECX MOV ] { } make ] unit-test
+[ { HEX: 4c HEX: 89 HEX: e2 } ] [ [ RDX R12 MOV ] { } make ] unit-test
+[ { HEX: 49 HEX: 89 HEX: d4 } ] [ [ R12 RDX MOV ] { } make ] unit-test
 
 [ { HEX: f2 HEX: 0f HEX: 2c HEX: c0 } ] [ [ EAX XMM0 CVTTSD2SI ] { } make ] unit-test
 [ { HEX: f2 HEX: 48 HEX: 0f HEX: 2c HEX: c0 } ] [ [ RAX XMM0 CVTTSD2SI ] { } make ] unit-test
@@ -39,3 +39,21 @@ IN: cpu.x86.assembler.tests
 
 [ { HEX: 80 HEX: 08 HEX: 05 } ] [ [ EAX [] 5 <byte> OR ] { } make ] unit-test
 [ { HEX: c6 HEX: 00 HEX: 05 } ] [ [ EAX [] 5 <byte> MOV ] { } make ] unit-test
+
+[ { HEX: 49 HEX: 89 HEX: 04 HEX: 1a } ] [ [ R10 RBX [+] RAX MOV ] { } make ] unit-test
+[ { HEX: 49 HEX: 89 HEX: 04 HEX: 1b } ] [ [ R11 RBX [+] RAX MOV ] { } make ] unit-test
+
+[ { HEX: 49 HEX: 89 HEX: 04 HEX: 1c } ] [ [ R12 RBX [+] RAX MOV ] { } make ] unit-test
+[ { HEX: 48 HEX: 89 HEX: 04 HEX: 1c } ] [ [ RSP RBX [+] RAX MOV ] { } make ] unit-test
+
+[ { HEX: 49 HEX: 89 HEX: 44 HEX: 1d HEX: 00 } ] [ [ R13 RBX [+] RAX MOV ] { } make ] unit-test
+[ { HEX: 48 HEX: 89 HEX: 44 HEX: 1d HEX: 00 } ] [ [ RBP RBX [+] RAX MOV ] { } make ] unit-test
+
+[ { HEX: 4a HEX: 89 HEX: 04 HEX: 23 } ] [ [ RBX R12 [+] RAX MOV ] { } make ] unit-test
+[ { HEX: 4a HEX: 89 HEX: 04 HEX: 2b } ] [ [ RBX R13 [+] RAX MOV ] { } make ] unit-test
+
+[ { HEX: 4b HEX: 89 HEX: 44 HEX: 25 HEX: 00 } ] [ [ R13 R12 [+] RAX MOV ] { } make ] unit-test
+[ { HEX: 4b HEX: 89 HEX: 04 HEX: 2c } ] [ [ R12 R13 [+] RAX MOV ] { } make ] unit-test
+
+[ { HEX: 49 HEX: 89 HEX: 04 HEX: 2c } ] [ [ R12 RBP [+] RAX MOV ] { } make ] unit-test
+[ [ R12 RSP [+] RAX MOV ] { } make ] must-fail
diff --git a/basis/cpu/x86/assembler/assembler.factor b/basis/cpu/x86/assembler/assembler.factor
index f557bb4adc..8cb0d620af 100644
--- a/basis/cpu/x86/assembler/assembler.factor
+++ b/basis/cpu/x86/assembler/assembler.factor
@@ -64,18 +64,18 @@ M: indirect extended? base>> extended? ;
 
 : canonicalize-EBP ( indirect -- indirect )
     #! { EBP } ==> { EBP 0 }
-    dup base>> { EBP RBP R13 } member? [
-        dup displacement>> [ 0 >>displacement ] unless
-    ] when ;
+    dup [ base>> { EBP RBP R13 } member? ] [ displacement>> not ] bi and
+    [ 0 >>displacement ] when ;
 
-: canonicalize-ESP ( indirect -- indirect )
-    #! { ESP } ==> { ESP ESP }
-    dup base>> { ESP RSP R12 } member? [ ESP >>index ] when ;
+ERROR: bad-index indirect ;
+
+: check-ESP ( indirect -- indirect )
+    dup index>> { ESP RSP } memq? [ bad-index ] when ;
 
 : canonicalize ( indirect -- indirect )
     #! Modify the indirect to work around certain addressing mode
     #! quirks.
-    canonicalize-EBP canonicalize-ESP ;
+    canonicalize-EBP check-ESP ;
 
 : <indirect> ( base index scale displacement -- indirect )
     indirect boa canonicalize ;
@@ -91,7 +91,7 @@ M: indirect extended? base>> extended? ;
 GENERIC: sib-present? ( op -- ? )
 
 M: indirect sib-present?
-    [ base>> { ESP RSP } member? ] [ index>> ] [ scale>> ] tri or or ;
+    [ base>> { ESP RSP R12 } member? ] [ index>> ] [ scale>> ] tri or or ;
 
 M: register sib-present? drop f ;
 
@@ -254,7 +254,8 @@ M: object operand-64? drop f ;
     reg-code swap addressing ;
 
 : direction-bit ( dst src op -- dst' src' op' )
-    pick register? [ BIN: 10 opcode-or swapd ] when ;
+    pick register? pick register? not and
+    [ BIN: 10 opcode-or swapd ] when ;
 
 : operand-size-bit ( dst src op -- dst' src' op' )
     over register-8? [ BIN: 1 opcode-or ] unless ;