diff --git a/src/libcore/core.rc b/src/libcore/core.rc
index da13145b9f6..eab66bc0e37 100644
--- a/src/libcore/core.rc
+++ b/src/libcore/core.rc
@@ -225,6 +225,8 @@ pub const debug : u32 = 4_u32;
 // The runtime interface used by the compiler
 #[cfg(notest)] pub mod rt;
 // The runtime and compiler interface to fmt!
+#[cfg(stage0)]
+#[path = "private/extfmt.rs"]
 pub mod extfmt;
 // Private APIs
 pub mod private;
diff --git a/src/libcore/prelude.rs b/src/libcore/prelude.rs
index b50fa265f03..1b2bfef5ecd 100644
--- a/src/libcore/prelude.rs
+++ b/src/libcore/prelude.rs
@@ -52,7 +52,6 @@ pub use char;
 pub use cmp;
 pub use dvec;
 pub use either;
-pub use extfmt;
 pub use f32;
 pub use f64;
 pub use float;
diff --git a/src/libcore/private.rs b/src/libcore/private.rs
index 61f2e013aba..a2656a9f73b 100644
--- a/src/libcore/private.rs
+++ b/src/libcore/private.rs
@@ -34,6 +34,8 @@ pub mod weak_task;
 pub mod exchange_alloc;
 #[path = "private/intrinsics.rs"]
 pub mod intrinsics;
+#[path = "private/extfmt.rs"]
+pub mod extfmt;
 
 extern mod rustrt {
     pub unsafe fn rust_create_little_lock() -> rust_little_lock;
diff --git a/src/libcore/extfmt.rs b/src/libcore/private/extfmt.rs
similarity index 100%
rename from src/libcore/extfmt.rs
rename to src/libcore/private/extfmt.rs
diff --git a/src/libsyntax/ext/fmt.rs b/src/libsyntax/ext/fmt.rs
index d967912221d..2c1a18fa882 100644
--- a/src/libsyntax/ext/fmt.rs
+++ b/src/libsyntax/ext/fmt.rs
@@ -23,7 +23,7 @@ use codemap::span;
 use ext::base::*;
 use ext::base;
 use ext::build::*;
-use extfmt::ct::*;
+use private::extfmt::ct::*;
 
 pub fn expand_syntax_ext(cx: ext_ctxt, sp: span, tts: ~[ast::token_tree])
     -> base::MacResult {
@@ -56,8 +56,8 @@ fn pieces_to_expr(cx: ext_ctxt, sp: span,
    -> @ast::expr {
     fn make_path_vec(cx: ext_ctxt, ident: @~str) -> ~[ast::ident] {
         let intr = cx.parse_sess().interner;
-        return ~[intr.intern(@~"extfmt"), intr.intern(@~"rt"),
-                 intr.intern(ident)];
+        return ~[intr.intern(@~"private"), intr.intern(@~"extfmt"),
+                 intr.intern(@~"rt"), intr.intern(ident)];
     }
     fn make_rt_path_expr(cx: ext_ctxt, sp: span, nm: @~str) -> @ast::expr {
         let path = make_path_vec(cx, nm);