diff --git a/build.rs b/build.rs
index 183b47ffd70f3..0ee39951c0723 100644
--- a/build.rs
+++ b/build.rs
@@ -20,7 +20,6 @@ const ALLOWED_CFGS: &'static [&'static str] = &[
     "libc_deny_warnings",
     "libc_long_array",
     "libc_non_exhaustive",
-    "libc_packedN",
     "libc_ptr_addr_of",
     "libc_thread_local",
     "libc_underscore_const_names",
@@ -85,9 +84,8 @@ fn main() {
         set_cfg("libc_deny_warnings");
     }
 
-    // Rust >= 1.33 supports repr(packed(N)) and cfg(target_vendor).
+    // Rust >= 1.33 supports cfg(target_vendor).
     if rustc_minor_ver >= 33 || rustc_dep_of_std {
-        set_cfg("libc_packedN");
         set_cfg("libc_cfg_target_vendor");
     }
 
diff --git a/libc-test/build.rs b/libc-test/build.rs
index 166726eaf6fbd..0dec4bba362f5 100644
--- a/libc-test/build.rs
+++ b/libc-test/build.rs
@@ -67,7 +67,7 @@ fn do_ctest() {
 
 fn ctest_cfg() -> ctest::TestGenerator {
     let mut cfg = ctest::TestGenerator::new();
-    let libc_cfgs = ["libc_packedN", "libc_thread_local"];
+    let libc_cfgs = ["libc_thread_local"];
     for f in &libc_cfgs {
         cfg.cfg(f, None);
     }
diff --git a/src/unix/bsd/apple/mod.rs b/src/unix/bsd/apple/mod.rs
index efac489dcfc30..7ed887753c971 100644
--- a/src/unix/bsd/apple/mod.rs
+++ b/src/unix/bsd/apple/mod.rs
@@ -1193,13 +1193,13 @@ s! {
 }
 
 s_no_extra_traits! {
-    #[cfg_attr(libc_packedN, repr(packed(4)))]
+    #[repr(packed(4))]
     pub struct ifconf {
         pub ifc_len: ::c_int,
         pub ifc_ifcu: __c_anonymous_ifc_ifcu,
     }
 
-    #[cfg_attr(libc_packedN, repr(packed(4)))]
+    #[repr(packed(4))]
     pub struct kevent {
         pub ident: ::uintptr_t,
         pub filter: i16,
@@ -1209,7 +1209,7 @@ s_no_extra_traits! {
         pub udata: *mut ::c_void,
     }
 
-    #[cfg_attr(libc_packedN, repr(packed(4)))]
+    #[repr(packed(4))]
     pub struct semid_ds {
         // Note the manpage shows different types than the system header.
         pub sem_perm: ipc_perm,
@@ -1222,7 +1222,7 @@ s_no_extra_traits! {
         pub sem_pad3: [i32; 4],
     }
 
-    #[cfg_attr(libc_packedN, repr(packed(4)))]
+    #[repr(packed(4))]
     pub struct shmid_ds {
         pub shm_perm: ipc_perm,
         pub shm_segsz: ::size_t,
@@ -1381,7 +1381,7 @@ s_no_extra_traits! {
         pub pth_name: [::c_char; MAXTHREADNAMESIZE],
     }
 
-    #[cfg_attr(libc_packedN, repr(packed(4)))]
+    #[repr(packed(4))]
     pub struct if_data64 {
         pub ifi_type: ::c_uchar,
         pub ifi_typelen: ::c_uchar,
@@ -1413,7 +1413,7 @@ s_no_extra_traits! {
         pub ifi_lastchange: timeval32,
     }
 
-    #[cfg_attr(libc_packedN, repr(packed(4)))]
+    #[repr(packed(4))]
     pub struct if_msghdr2 {
         pub ifm_msglen: ::c_ushort,
         pub ifm_version: ::c_uchar,
@@ -1428,7 +1428,7 @@ s_no_extra_traits! {
         pub ifm_data: if_data64,
     }
 
-    #[cfg_attr(libc_packedN, repr(packed(8)))]
+    #[repr(packed(8))]
     pub struct vm_statistics64 {
         pub free_count: natural_t,
         pub active_count: natural_t,
@@ -1456,7 +1456,7 @@ s_no_extra_traits! {
         pub total_uncompressed_pages_in_compressor: u64,
     }
 
-    #[cfg_attr(libc_packedN, repr(packed(4)))]
+    #[repr(packed(4))]
     pub struct mach_task_basic_info {
         pub virtual_size: mach_vm_size_t,
         pub resident_size: mach_vm_size_t,
@@ -1467,7 +1467,7 @@ s_no_extra_traits! {
         pub suspend_count: integer_t,
     }
 
-    #[cfg_attr(libc_packedN, repr(packed(4)))]
+    #[repr(packed(4))]
     pub struct log2phys {
         pub l2p_flags: ::c_uint,
         pub l2p_contigbytes: ::off_t,
@@ -1478,7 +1478,7 @@ s_no_extra_traits! {
         _os_unfair_lock_opaque: u32,
     }
 
-   #[cfg_attr(libc_packedN, repr(packed(1)))]
+   #[repr(packed(1))]
     pub struct sockaddr_vm {
         pub svm_len: ::c_uchar,
         pub svm_family: ::sa_family_t,
@@ -1498,7 +1498,7 @@ s_no_extra_traits! {
         pub ifk_value: ::c_int,
     }
 
-    #[cfg_attr(libc_packedN, repr(packed(4)))]
+    #[repr(packed(4))]
     pub struct ifkpi {
         pub ifk_module_id: ::c_uint,
         pub ifk_type: ::c_uint,
diff --git a/src/unix/solarish/illumos.rs b/src/unix/solarish/illumos.rs
index 62a07f6279030..07cc583f43f3d 100644
--- a/src/unix/solarish/illumos.rs
+++ b/src/unix/solarish/illumos.rs
@@ -46,10 +46,7 @@ s! {
 }
 
 s_no_extra_traits! {
-    #[cfg_attr(any(
-        target_arch = "x86", target_arch = "x86_64"),
-        repr(packed(4))
-    )]
+    #[cfg_attr(any(target_arch = "x86", target_arch = "x86_64"), repr(packed(4)))]
     pub struct epoll_event {
         pub events: u32,
         pub u64: u64,