diff --git a/core/cpu/x86/64/64.factor b/core/cpu/x86/64/64.factor
index 956439262a..55513b0930 100644
--- a/core/cpu/x86/64/64.factor
+++ b/core/cpu/x86/64/64.factor
@@ -4,7 +4,7 @@ USING: alien.c-types arrays cpu.x86.assembler
 cpu.x86.architecture cpu.x86.intrinsics cpu.x86.sse2
 cpu.x86.allot cpu.architecture kernel kernel.private math
 namespaces sequences generator.registers generator.fixup system
-alien ;
+alien alien.compiler alien.structs slots splitting math.functions ;
 IN: cpu.x86.64
 
 PREDICATE: x86-backend amd64-backend
@@ -178,10 +178,10 @@ T{ x86-backend f 8 } compiler-backend set-global
 
 ! The ABI for passing structs by value is pretty messed up
 "void*" c-type clone "__stack_value" define-primitive-type
-T{ stack-regs } "__stack_value" c-type set-c-type-reg-class
+T{ stack-params } "__stack_value" c-type set-c-type-reg-class
 
-: struct-types&offset ( ctype -- pairs )
-    c-type struct-type-fields [
+: struct-types&offset ( struct-type -- pairs )
+    struct-type-fields [
         dup slot-spec-type swap slot-spec-offset 2array
     ] map ;
 
@@ -192,14 +192,15 @@ T{ stack-regs } "__stack_value" c-type set-c-type-reg-class
 
 : flatten-large-struct ( type -- )
     heap-size cell align
-    cell /i "__stack_value" <repetition> % ;
+    cell /i "__stack_value" c-type <repetition> % ;
 
 M: struct-type flatten-value-type ( type -- seq )
-    dup c-size 16 > [
+    dup heap-size 16 > [
         flatten-large-struct
     ] [
         struct-types&offset split-struct [
             [ c-type c-type-reg-class ] map
-            T{ int-regs } swap member? "void*" "double" ? ,
+            T{ int-regs } swap member?
+            "void*" "double" ? c-type ,
         ] each
     ] if ;