diff --git a/lib/std/builtin.zig b/lib/std/builtin.zig
index eda7f0ff4f..91ef1c38f9 100644
--- a/lib/std/builtin.zig
+++ b/lib/std/builtin.zig
@@ -613,10 +613,10 @@ 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(u2) {
-            One,
-            Many,
-            Slice,
-            C,
+            one,
+            many,
+            slice,
+            c,
         };
     };