diff --git a/libc-test/build.rs b/libc-test/build.rs
index 3f7e1d73587bf..794dadaa676f1 100644
--- a/libc-test/build.rs
+++ b/libc-test/build.rs
@@ -4427,8 +4427,6 @@ fn test_linux(target: &str) {
     cfg.skip_roundtrip(move |s| match s {
         // FIXME:
         "mcontext_t" if s390x => true,
-        // FIXME: This is actually a union.
-        "fpreg_t" if s390x => true,
 
         // The test doesn't work on some env:
         "ipv6_mreq"
diff --git a/src/unix/linux_like/linux/gnu/b64/s390x.rs b/src/unix/linux_like/linux/gnu/b64/s390x.rs
index 4c31252fbad30..c539c2b0d338b 100644
--- a/src/unix/linux_like/linux/gnu/b64/s390x.rs
+++ b/src/unix/linux_like/linux/gnu/b64/s390x.rs
@@ -212,33 +212,17 @@ s! {
 }
 
 s_no_extra_traits! {
-    // FIXME: This is actually a union.
-    pub struct fpreg_t {
+    pub union fpreg_t {
         pub d: ::c_double,
-        // f: ::c_float,
+        pub f: ::c_float,
     }
 }
 
 cfg_if! {
     if #[cfg(feature = "extra_traits")] {
-        impl PartialEq for fpreg_t {
-            fn eq(&self, other: &fpreg_t) -> bool {
-                self.d == other.d
-            }
-        }
-
-        impl Eq for fpreg_t {}
-
         impl ::fmt::Debug for fpreg_t {
             fn fmt(&self, f: &mut ::fmt::Formatter) -> ::fmt::Result {
-                f.debug_struct("fpreg_t").field("d", &self.d).finish()
-            }
-        }
-
-        impl ::hash::Hash for fpreg_t {
-            fn hash<H: ::hash::Hasher>(&self, state: &mut H) {
-                let d: u64 = unsafe { ::mem::transmute(self.d) };
-                d.hash(state);
+                f.finish_non_exhaustive()
             }
         }
     }