no need to use NonNull

.travis.yml

@@ -1,7 +1,7 @@
 sudo: false
 language: rust
 rust:
-  - 1.25.0  # Oldest supported (to make doc-comment not ICE)
+  - 1.20.0  # Oldest supported
   - 1.36.0  # Oldest supported with MaybeUninit
   - stable
   - beta

README.md

@@ -18,7 +18,7 @@ Add the following dependency to your `Cargo.toml`:
 memoffset = "0.5"
 ```
 
-These versions will compile fine with rustc versions greater or equal to 1.25.
+These versions will compile fine with rustc versions greater or equal to 1.20.
 
 Add the following lines at the top of your `main.rs` or `lib.rs` files.
 

src/offset_of.rs

@@ -39,10 +39,9 @@ macro_rules! _memoffset__let_base_ptr {
 #[doc(hidden)]
 macro_rules! _memoffset__let_base_ptr {
     ($name:ident, $type:tt) => {
-        // No UB right here, but we will later offset into a field
-        // of this pointer, and that is UB when the pointer is dangling.
-        let non_null = $crate::ptr::NonNull::<$type>::dangling();
-        let $name = non_null.as_ptr() as *const $type;
+        // No UB right here, but we will later dereference this pointer to
+        // offset into a field, and that is UB when the pointer is dangling.
+        let $name = $crate::mem::align_of::<$type>() as *const $type;
     };
 }