diff --git a/lib/std/builtin.zig b/lib/std/builtin.zig
index ec69270d15..ff6d20370c 100644
--- a/lib/std/builtin.zig
+++ b/lib/std/builtin.zig
@@ -190,7 +190,7 @@ pub const CallingConvention = enum {
 
 /// This data structure is used by the Zig language code generation and
 /// therefore must be kept in sync with the compiler implementation.
-pub const AddressSpace = enum {
+pub const AddressSpace = enum(u4) {
     generic,
     gs,
     fs,
@@ -283,7 +283,7 @@ pub const Type = union(enum) {
 
         /// This data structure is used by the Zig language code generation and
         /// therefore must be kept in sync with the compiler implementation.
-        pub const Size = enum {
+        pub const Size = enum(u2) {
             One,
             Many,
             Slice,