diff --git a/clippy_lints/src/derive.rs b/clippy_lints/src/derive.rs
index 2311df424..17d17a445 100644
--- a/clippy_lints/src/derive.rs
+++ b/clippy_lints/src/derive.rs
@@ -141,7 +141,7 @@ fn check_copy_clone<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, item: &Item, trait_ref
         }
 
         match ty.sty {
-            //FIXME:unions: TypeVariants::TyUnion(..) => return,
+            TypeVariants::TyUnion(..) => return,
 
             // Some types are not Clone by default but could be cloned “by hand” if necessary
             TypeVariants::TyEnum(def, substs) |
diff --git a/clippy_lints/src/len_zero.rs b/clippy_lints/src/len_zero.rs
index fbcae0878..f574e6b7f 100644
--- a/clippy_lints/src/len_zero.rs
+++ b/clippy_lints/src/len_zero.rs
@@ -215,8 +215,8 @@ fn has_is_empty(cx: &LateContext, expr: &Expr) -> bool {
         }
         ty::TyProjection(_) => ty.ty_to_def_id().map_or(false, |id| has_is_empty_impl(cx, &id)),
         ty::TyEnum(id, _) |
-        ty::TyStruct(id, _) /*FIXME:unions: |
-        ty::TyUnion(id, _)*/ => has_is_empty_impl(cx, &id.did),
+        ty::TyStruct(id, _) |
+        ty::TyUnion(id, _) => has_is_empty_impl(cx, &id.did),
         ty::TyArray(..) | ty::TyStr => true,
         _ => false,
     }
diff --git a/clippy_lints/src/missing_doc.rs b/clippy_lints/src/missing_doc.rs
index bd6354ad9..454f59175 100644
--- a/clippy_lints/src/missing_doc.rs
+++ b/clippy_lints/src/missing_doc.rs
@@ -123,7 +123,7 @@ impl LateLintPass for MissingDoc {
             hir::ItemStruct(..) => "a struct",
             hir::ItemTrait(..) => "a trait",
             hir::ItemTy(..) => "a type alias",
-            //FIXME:unions: hir::ItemUnion(..) => "a union",
+            hir::ItemUnion(..) => "a union",
             hir::ItemDefaultImpl(..) |
             hir::ItemExternCrate(..) |
             hir::ItemForeignMod(..) |
diff --git a/tests/compile-fail/derive.rs b/tests/compile-fail/derive.rs
index 39d9dde28..cf4467f30 100644
--- a/tests/compile-fail/derive.rs
+++ b/tests/compile-fail/derive.rs
@@ -1,7 +1,7 @@
 #![feature(plugin)]
 #![plugin(clippy)]
 
-//FIXME:unions: #![feature(untagged_unions)]
+#![feature(untagged_unions)]
 
 #![deny(warnings)]
 #![allow(dead_code)]
@@ -47,7 +47,6 @@ impl Clone for Qux {
     fn clone(&self) -> Self { Qux }
 }
 
-/* FIXME:unions
 // looks like unions don't support deriving Clone for now
 #[derive(Copy)]
 union Union {
@@ -61,7 +60,6 @@ impl Clone for Union {
         }
     }
 }
-*/
 
 // See #666
 #[derive(Copy)]
diff --git a/tests/compile-fail/no_effect.rs b/tests/compile-fail/no_effect.rs
index 39b59a599..6616f7bdc 100644
--- a/tests/compile-fail/no_effect.rs
+++ b/tests/compile-fail/no_effect.rs
@@ -4,7 +4,7 @@
 #![deny(no_effect, unnecessary_operation)]
 #![allow(dead_code)]
 #![allow(path_statements)]
-//FIXME:unions #![feature(untagged_unions)]
+#![feature(untagged_unions)]
 
 struct Unit;
 struct Tuple(i32);
@@ -16,12 +16,10 @@ enum Enum {
     Struct { field: i32 },
 }
 
-/*FIXME:unions:
 union Union {
     a: u8,
     b: f64,
 }
-*/
 
 fn get_number() -> i32 { 0 }
 fn get_struct() -> Struct { Struct { field: 0 } }
@@ -38,7 +36,7 @@ fn main() {
     Tuple(0); //~ERROR statement with no effect
     Struct { field: 0 }; //~ERROR statement with no effect
     Struct { ..s }; //~ERROR statement with no effect
-    //FIXME:unions: Union { a: 0 }; // /**FIXME*~***/ ERROR statement with no effect
+    Union { a: 0 }; //~ERROR statement with no effect
     Enum::Tuple(0); //~ERROR statement with no effect
     Enum::Struct { field: 0 }; //~ERROR statement with no effect
     5 + 6; //~ERROR statement with no effect