diff --git a/xtask/src/check_raw.rs b/xtask/src/check_raw.rs
index 1702fe04d..b6887afc6 100644
--- a/xtask/src/check_raw.rs
+++ b/xtask/src/check_raw.rs
@@ -16,8 +16,8 @@ use syn::spanned::Spanned;
 use syn::token::Comma;
 use syn::{
     parenthesized, Abi, Attribute, Field, Fields, FieldsNamed, FieldsUnnamed, File, Item,
-    ItemConst, ItemMacro, ItemStruct, ItemType, LitInt, ReturnType, Type, TypeArray, TypeBareFn,
-    TypePtr, Visibility,
+    ItemConst, ItemMacro, ItemStruct, ItemType, ItemUnion, LitInt, ReturnType, Type, TypeArray,
+    TypeBareFn, TypePtr, Visibility,
 };
 use walkdir::WalkDir;
 
@@ -253,26 +253,46 @@ fn check_fields(fields: &Punctuated<Field, Comma>, src: &Path) -> Result<(), Err
     Ok(())
 }
 
+fn check_type_attrs(attrs: &[Attribute], spanned: &dyn Spanned, src: &Path) -> Result<(), Error> {
+    let attrs = parse_attrs(attrs, src)?;
+    let reprs = get_reprs(&attrs);
+
+    let allowed_reprs: &[&[Repr]] = &[&[Repr::C], &[Repr::C, Repr::Packed], &[Repr::Transparent]];
+
+    if allowed_reprs.contains(&reprs.as_slice()) {
+        Ok(())
+    } else {
+        Err(Error::new(ErrorKind::ForbiddenRepr, src, spanned))
+    }
+}
+
 /// Validate a struct.
 fn check_struct(item: &ItemStruct, src: &Path) -> Result<(), Error> {
     if !is_pub(&item.vis) {
         return Err(Error::new(ErrorKind::MissingPub, src, &item.struct_token));
     }
 
-    let attrs = parse_attrs(&item.attrs, src)?;
-
     match &item.fields {
         Fields::Named(FieldsNamed { named, .. }) => check_fields(named, src)?,
         Fields::Unnamed(FieldsUnnamed { unnamed, .. }) => check_fields(unnamed, src)?,
         Fields::Unit => {}
     }
 
-    let reprs = get_reprs(&attrs);
-    let allowed_reprs: &[&[Repr]] = &[&[Repr::C], &[Repr::C, Repr::Packed], &[Repr::Transparent]];
-    if !allowed_reprs.contains(&reprs.as_slice()) {
-        return Err(Error::new(ErrorKind::ForbiddenRepr, src, item));
+    check_type_attrs(&item.attrs, item, src)?;
+
+    Ok(())
+}
+
+/// Validate a union.
+fn check_union(item: &ItemUnion, src: &Path) -> Result<(), Error> {
+    if !is_pub(&item.vis) {
+        return Err(Error::new(ErrorKind::MissingPub, src, &item.union_token));
     }
 
+    check_fields(&item.fields.named, src)?;
+
+    check_type_attrs(&item.attrs, item, src)?;
+
     Ok(())
 }
 
@@ -319,6 +339,9 @@ fn check_item(item: &Item, src: &Path) -> Result<(), Error> {
         Item::Struct(item) => {
             check_struct(item, src)?;
         }
+        Item::Union(item) => {
+            check_union(item, src)?;
+        }
         Item::Macro(item) => {
             check_macro(item, src)?;
         }
@@ -555,4 +578,52 @@ mod tests {
             ErrorKind::ForbiddenType,
         );
     }
+
+    #[test]
+    fn test_union() {
+        // Valid union.
+        assert!(check_union(
+            &parse_quote! {
+                #[repr(C)]
+                pub union U {
+                    pub a: u32,
+                    pub b: u64,
+                }
+            },
+            src(),
+        )
+        .is_ok());
+
+        // Missing `pub` on union.
+        check_item_err(
+            parse_quote! {
+                #[repr(C)]
+                struct U {
+                    pub f: u32,
+                }
+            },
+            ErrorKind::MissingPub,
+        );
+
+        // Missing `pub` on field.
+        check_item_err(
+            parse_quote! {
+                #[repr(C)]
+                pub struct U {
+                    f: u32,
+                }
+            },
+            ErrorKind::MissingPub,
+        );
+
+        // Forbidden `repr`.
+        check_item_err(
+            parse_quote! {
+                pub struct S {
+                    pub f: u32,
+                }
+            },
+            ErrorKind::ForbiddenRepr,
+        );
+    }
 }