diff --git a/src/interpreter.rs b/src/interpreter.rs
index e9c581a5681..8741beb8735 100644
--- a/src/interpreter.rs
+++ b/src/interpreter.rs
@@ -13,7 +13,7 @@ use syntax::codemap::DUMMY_SP;
 
 use error::EvalResult;
 use memory::{self, FieldRepr, Memory, Pointer, Repr};
-use primval::{self, PrimVal};
+use primval;
 
 const TRACE_EXECUTION: bool = true;
 
@@ -242,11 +242,8 @@ impl<'a, 'tcx: 'a> Interpreter<'a, 'tcx> {
                                 match &self.tcx.item_name(def_id).as_str()[..] {
                                     "size_of" => {
                                         let ty = *substs.types.get(subst::FnSpace, 0);
-                                        let size = PrimVal::from_usize(
-                                            self.ty_to_repr(ty).size(),
-                                            &dest_repr
-                                        );
-                                        try!(self.memory.write_primval(dest, size));
+                                        let size = self.ty_to_repr(ty).size() as u64;
+                                        try!(self.memory.write_uint(dest, size, dest_repr.size()));
                                     }
 
                                     "offset" => {
diff --git a/src/memory.rs b/src/memory.rs
index 73bdc4ea49a..17e9439de6d 100644
--- a/src/memory.rs
+++ b/src/memory.rs
@@ -184,6 +184,10 @@ impl Memory {
             ty::TyUint(UintTy::U16) => self.read_u16(ptr).map(PrimVal::U16),
             ty::TyUint(UintTy::U32) => self.read_u32(ptr).map(PrimVal::U32),
             ty::TyUint(UintTy::U64) => self.read_u64(ptr).map(PrimVal::U64),
+
+            // TODO(tsion): Pick the PrimVal dynamically.
+            ty::TyInt(IntTy::Is)    => self.read_int(ptr, POINTER_SIZE).map(PrimVal::I64),
+            ty::TyUint(UintTy::Us)  => self.read_uint(ptr, POINTER_SIZE).map(PrimVal::U64),
             _ => panic!("primitive read of non-primitive type: {:?}", ty),
         }
     }
@@ -255,6 +259,14 @@ impl Memory {
         Ok(())
     }
 
+    pub fn read_int(&self, ptr: Pointer, size: usize) -> EvalResult<i64> {
+        self.get_bytes(ptr, size).map(|mut b| b.read_int::<NativeEndian>(size).unwrap())
+    }
+
+    pub fn write_int(&mut self, ptr: Pointer, n: i64, size: usize) -> EvalResult<()> {
+        self.get_bytes_mut(ptr, size).map(|mut b| b.write_int::<NativeEndian>(n, size).unwrap())
+    }
+
     pub fn read_u8(&self, ptr: Pointer) -> EvalResult<u8> {
         self.get_bytes(ptr, 1).map(|b| b[0] as u8)
     }
diff --git a/src/primval.rs b/src/primval.rs
index 88bd88b1746..a34da06d597 100644
--- a/src/primval.rs
+++ b/src/primval.rs
@@ -1,7 +1,5 @@
 use rustc::mir::repr as mir;
 
-use memory::Repr;
-
 #[derive(Clone, Copy, Debug, PartialEq)]
 pub enum PrimVal {
     Bool(bool),
@@ -9,29 +7,6 @@ pub enum PrimVal {
     U8(u8), U16(u16), U32(u32), U64(u64),
 }
 
-impl PrimVal {
-    pub fn from_usize(n: usize, repr: &Repr) -> Self {
-        // TODO(tsion): Use checked casts.
-        match *repr {
-            Repr::U8  => PrimVal::U8(n as u8),
-            Repr::U16 => PrimVal::U16(n as u16),
-            Repr::U32 => PrimVal::U32(n as u32),
-            Repr::U64 => PrimVal::U64(n as u64),
-            _ => panic!("attempted to make usize primval from non-uint repr"),
-        }
-    }
-
-    pub fn to_usize(self) -> usize {
-        match self {
-            PrimVal::U8(n)  => n as usize,
-            PrimVal::U16(n) => n as usize,
-            PrimVal::U32(n) => n as usize,
-            PrimVal::U64(n) => n as usize,
-            _ => panic!("attempted to make usize from non-uint primval"),
-        }
-    }
-}
-
 pub fn binary_op(bin_op: mir::BinOp, left: PrimVal, right: PrimVal) -> PrimVal {
     macro_rules! int_binops {
         ($v:ident, $l:ident, $r:ident) => ({