diff --git a/src/libsyntax/ast.rs b/src/libsyntax/ast.rs
index a2c859cf9fd3..1edcb35289a3 100644
--- a/src/libsyntax/ast.rs
+++ b/src/libsyntax/ast.rs
@@ -119,7 +119,7 @@ impl Name {
     pub fn as_str<'a>(&'a self) -> &'a str {
         unsafe {
             // FIXME #12938: can't use copy_lifetime since &str isn't a &T
-            ::std::mem::transmute(token::get_name(*self).get())
+            ::std::mem::transmute::<&str,&str>(token::get_name(*self).get())
         }
     }
 
diff --git a/src/libsyntax/parse/token.rs b/src/libsyntax/parse/token.rs
index d56aa8da72a8..615cd34ca14d 100644
--- a/src/libsyntax/parse/token.rs
+++ b/src/libsyntax/parse/token.rs
@@ -668,12 +668,12 @@ impl InternedString {
 
 impl BytesContainer for InternedString {
     fn container_as_bytes<'a>(&'a self) -> &'a [u8] {
-        // FIXME(pcwalton): This is a workaround for the incorrect signature
+        // FIXME #12938: This is a workaround for the incorrect signature
         // of `BytesContainer`, which is itself a workaround for the lack of
         // DST.
         unsafe {
             let this = self.get();
-            mem::transmute(this.container_as_bytes())
+            mem::transmute::<&[u8],&[u8]>(this.container_as_bytes())
         }
     }
 }
diff --git a/src/libsyntax/print/pprust.rs b/src/libsyntax/print/pprust.rs
index 386fd8ae5a61..4cfc95d4c3ff 100644
--- a/src/libsyntax/print/pprust.rs
+++ b/src/libsyntax/print/pprust.rs
@@ -169,17 +169,14 @@ pub fn to_string(f: |&mut State| -> IoResult<()>) -> String {
     let mut s = rust_printer(box MemWriter::new());
     f(&mut s).unwrap();
     eof(&mut s.s).unwrap();
-    unsafe {
+    let wr = unsafe {
         // FIXME(pcwalton): A nasty function to extract the string from an `io::Writer`
         // that we "know" to be a `MemWriter` that works around the lack of checked
         // downcasts.
-        let obj: TraitObject = mem::transmute_copy(&s.s.out);
-        let wr: Box<MemWriter> = mem::transmute(obj.data);
-        let result =
-            String::from_utf8(wr.get_ref().as_slice().to_vec()).unwrap();
-        mem::forget(wr);
-        result.to_string()
-    }
+        let obj: &TraitObject = mem::transmute(&s.s.out);
+        mem::transmute::<*mut (), &MemWriter>(obj.data)
+    };
+    String::from_utf8(wr.get_ref().to_vec()).unwrap()
 }
 
 pub fn binop_to_string(op: BinOpToken) -> &'static str {