diff --git a/src/libstd/rand/os.rs b/src/libstd/rand/os.rs
index 9ae9455848e59..bd31fe08421a6 100644
--- a/src/libstd/rand/os.rs
+++ b/src/libstd/rand/os.rs
@@ -205,9 +205,7 @@ mod imp {
         _dummy: (),
     }
 
-    // Fake definition; this is actually a struct, but we don't use the
-    // contents here.
-    type SecRandom = c_void;
+    enum SecRandom {}
 
     #[allow(non_upper_case_globals)]
     const kSecRandomDefault: *const SecRandom = 0 as *const SecRandom;
diff --git a/src/libstd/rt/unwind/seh64_gnu.rs b/src/libstd/rt/unwind/seh64_gnu.rs
index 6a061a55fc2a6..847ba47ff7251 100644
--- a/src/libstd/rt/unwind/seh64_gnu.rs
+++ b/src/libstd/rt/unwind/seh64_gnu.rs
@@ -60,8 +60,8 @@ pub struct EXCEPTION_RECORD {
     ExceptionInformation: [ULONG_PTR; 15],
 }
 
-pub type CONTEXT = c_void;
-pub type UNWIND_HISTORY_TABLE = c_void;
+pub enum CONTEXT {}
+pub enum UNWIND_HISTORY_TABLE {}
 
 #[repr(C)]
 pub struct RUNTIME_FUNCTION {