diff --git a/runtime/adainclude/interfaces.ads b/runtime/adainclude/interfaces.ads
index 4f56bb9..dc63d8d 100644
--- a/runtime/adainclude/interfaces.ads
+++ b/runtime/adainclude/interfaces.ads
@@ -1,18 +1,29 @@
 package Interfaces
    with Pure is
 
-   type Integer_32 is range -2**31 .. 2**31 - 1;
-   type Unsigned_32 is mod 2**32;
+   type Bit_1 is mod 2**1
+     with Size => 1;
+   type Bit_2 is mod 2**2
+     with Size => 2;
+   type Bit_3 is mod 2**3
+     with Size => 3;
+   type Bit_4 is mod 2**4
+     with Size => 4;
 
-   function Shift_Left (Value : Unsigned_32; Amount : Natural)
-      return Unsigned_32 with Import, Convention => Intrinsic;
-   function Shift_Right (Value : Unsigned_32; Amount : Natural)
-      return Unsigned_32 with Import, Convention => Intrinsic;
-   function Shift_Right_Arithmetic (Value : Unsigned_32; Amount : Natural)
-      return Unsigned_32 with Import, Convention => Intrinsic;
-   function Rotate_Left (Value : Unsigned_32; Amount : Natural)
-      return Unsigned_32 with Import, Convention => Intrinsic;
-   function Rotate_Right (Value : Unsigned_32; Amount : Natural)
-      return Unsigned_32 with Import, Convention => Intrinsic;
+   type Bit_31 is mod 2**32
+     with Size => 31;
+   type Bit_32 is mod 2**32
+     with Size => 32;
+
+   function Shift_Left (Value : Bit_32; Amount : Natural)
+      return Bit_32 with Import, Convention => Intrinsic;
+   function Shift_Right (Value : Bit_32; Amount : Natural)
+      return Bit_32 with Import, Convention => Intrinsic;
+   function Shift_Right_Arithmetic (Value : Bit_32; Amount : Natural)
+      return Bit_32 with Import, Convention => Intrinsic;
+   function Rotate_Left (Value : Bit_32; Amount : Natural)
+      return Bit_32 with Import, Convention => Intrinsic;
+   function Rotate_Right (Value : Bit_32; Amount : Natural)
+      return Bit_32 with Import, Convention => Intrinsic;
 
 end Interfaces;