diff --git a/src/codegen/impl_partialeq.rs b/src/codegen/impl_partialeq.rs
index 02783808..31c2c979 100644
--- a/src/codegen/impl_partialeq.rs
+++ b/src/codegen/impl_partialeq.rs
@@ -20,7 +20,7 @@ pub fn gen_partialeq_impl(
             &self._bindgen_opaque_blob[..] == &other._bindgen_opaque_blob[..]
         });
     } else if comp_info.kind() == CompKind::Union {
-        assert!(!ctx.options().rust_features().untagged_union());
+        assert!(!ctx.options().rust_features().untagged_union);
         tokens.push(quote! {
             &self.bindgen_union_field[..] == &other.bindgen_union_field[..]
         });
diff --git a/src/codegen/mod.rs b/src/codegen/mod.rs
index 950708a0..a6ab3997 100644
--- a/src/codegen/mod.rs
+++ b/src/codegen/mod.rs
@@ -1641,7 +1641,7 @@ impl CodeGenerator for CompInfo {
             attributes.push(attributes::repr("C"));
         }
 
-        if ctx.options().rust_features().repr_align() {
+        if ctx.options().rust_features().repr_align {
             if let Some(explicit) = explicit_align {
                 // Ensure that the struct has the correct alignment even in
                 // presence of alignas.
@@ -1671,7 +1671,7 @@ impl CodeGenerator for CompInfo {
         if item.can_derive_copy(ctx) && !item.annotations().disallow_copy() {
             derives.push("Copy");
 
-            if ctx.options().rust_features().builtin_clone_impls() ||
+            if ctx.options().rust_features().builtin_clone_impls ||
                 used_template_params.is_some()
             {
                 // FIXME: This requires extra logic if you have a big array in a
@@ -2012,7 +2012,7 @@ impl MethodCodegen for Method {
             _ => panic!("How in the world?"),
         };
 
-        if let (Abi::ThisCall, false) = (signature.abi(), ctx.options().rust_features().thiscall_abi()) {
+        if let (Abi::ThisCall, false) = (signature.abi(), ctx.options().rust_features().thiscall_abi) {
             return;
         }
 
@@ -3183,7 +3183,7 @@ impl TryToRustTy for FunctionSig {
         let abi = self.abi();
 
         match abi {
-            Abi::ThisCall if !ctx.options().rust_features().thiscall_abi() => {
+            Abi::ThisCall if !ctx.options().rust_features().thiscall_abi => {
                 warn!("Skipping function with thiscall ABI that isn't supported by the configured Rust target");
                 Ok(quote::Tokens::new())
             }
@@ -3280,7 +3280,7 @@ impl CodeGenerator for Function {
         }
 
         let abi = match signature.abi() {
-            Abi::ThisCall if !ctx.options().rust_features().thiscall_abi() => {
+            Abi::ThisCall if !ctx.options().rust_features().thiscall_abi => {
                 warn!("Skipping function with thiscall ABI that isn't supported by the configured Rust target");
                 return;
             }
diff --git a/src/features.rs b/src/features.rs
index fe4f8453..1b490f54 100644
--- a/src/features.rs
+++ b/src/features.rs
@@ -113,7 +113,10 @@ macro_rules! rust_feature_def {
         #[derive(Debug, Copy, Clone, Eq, PartialEq, Hash)]
         pub struct RustFeatures {
             $(
-                $feature: bool,
+                $(
+                    #[$attr]
+                )*
+                pub $feature: bool,
             )*
         }
 
@@ -126,15 +129,6 @@ macro_rules! rust_feature_def {
                     )*
                 }
             }
-
-            $(
-                $(
-                    #[$attr]
-                )*
-                pub fn $feature(&self) -> bool {
-                    self.$feature
-                }
-            )*
         }
     }
 }
diff --git a/src/ir/analysis/derive_copy.rs b/src/ir/analysis/derive_copy.rs
index 94d457d5..69725ead 100644
--- a/src/ir/analysis/derive_copy.rs
+++ b/src/ir/analysis/derive_copy.rs
@@ -234,7 +234,7 @@ impl<'ctx> MonotoneFramework for CannotDeriveCopy<'ctx> {
                 }
 
                 if info.kind() == CompKind::Union {
-                    if !self.ctx.options().rust_features().untagged_union() {
+                    if !self.ctx.options().rust_features().untagged_union {
                         // NOTE: If there's no template parameters we can derive
                         // copy unconditionally, since arrays are magical for
                         // rustc, and __BindgenUnionField always implements
diff --git a/src/ir/analysis/derive_debug.rs b/src/ir/analysis/derive_debug.rs
index a1743ae9..b191d37d 100644
--- a/src/ir/analysis/derive_debug.rs
+++ b/src/ir/analysis/derive_debug.rs
@@ -150,7 +150,7 @@ impl<'ctx> MonotoneFramework for CannotDeriveDebug<'ctx> {
             });
             return if layout_can_derive &&
                       !(ty.is_union() &&
-                        self.ctx.options().rust_features().untagged_union()) {
+                        self.ctx.options().rust_features().untagged_union) {
                 trace!("    we can trivially derive Debug for the layout");
                 ConstrainResult::Same
             } else {
@@ -235,7 +235,7 @@ impl<'ctx> MonotoneFramework for CannotDeriveDebug<'ctx> {
                 );
 
                 if info.kind() == CompKind::Union {
-                    if self.ctx.options().rust_features().untagged_union() {
+                    if self.ctx.options().rust_features().untagged_union {
                         trace!("    cannot derive Debug for Rust unions");
                         return self.insert(id);
                     }
diff --git a/src/ir/analysis/derive_default.rs b/src/ir/analysis/derive_default.rs
index 2c79a437..e319166d 100644
--- a/src/ir/analysis/derive_default.rs
+++ b/src/ir/analysis/derive_default.rs
@@ -177,7 +177,7 @@ impl<'ctx> MonotoneFramework for CannotDeriveDefault<'ctx> {
             });
             return if layout_can_derive &&
                       !(ty.is_union() &&
-                        self.ctx.options().rust_features().untagged_union()) {
+                        self.ctx.options().rust_features().untagged_union) {
                 trace!("    we can trivially derive Default for the layout");
                 ConstrainResult::Same
             } else {
@@ -271,7 +271,7 @@ impl<'ctx> MonotoneFramework for CannotDeriveDefault<'ctx> {
                 }
 
                 if info.kind() == CompKind::Union {
-                    if self.ctx.options().rust_features().untagged_union() {
+                    if self.ctx.options().rust_features().untagged_union {
                         trace!("    cannot derive Default for Rust unions");
                         return self.insert(id);
                     }
diff --git a/src/ir/analysis/derive_hash.rs b/src/ir/analysis/derive_hash.rs
index 3fc31b39..c23a891e 100644
--- a/src/ir/analysis/derive_hash.rs
+++ b/src/ir/analysis/derive_hash.rs
@@ -137,7 +137,7 @@ impl<'ctx> MonotoneFramework for CannotDeriveHash<'ctx> {
             });
             return if layout_can_derive &&
                 !(ty.is_union() &&
-                  self.ctx.options().rust_features().untagged_union()) {
+                  self.ctx.options().rust_features().untagged_union) {
                 trace!("    we can trivially derive Hash for the layout");
                 ConstrainResult::Same
             } else {
@@ -257,7 +257,7 @@ impl<'ctx> MonotoneFramework for CannotDeriveHash<'ctx> {
                 }
 
                 if info.kind() == CompKind::Union {
-                    if self.ctx.options().rust_features().untagged_union() {
+                    if self.ctx.options().rust_features().untagged_union {
                         trace!("    cannot derive Hash for Rust unions");
                         return self.insert(id);
                     }
diff --git a/src/ir/analysis/derive_partialeq_or_partialord.rs b/src/ir/analysis/derive_partialeq_or_partialord.rs
index 2641d2b3..cebdceef 100644
--- a/src/ir/analysis/derive_partialeq_or_partialord.rs
+++ b/src/ir/analysis/derive_partialeq_or_partialord.rs
@@ -119,7 +119,7 @@ impl<'ctx> CannotDerivePartialEqOrPartialOrd<'ctx> {
         trace!("ty: {:?}", ty);
         if item.is_opaque(self.ctx, &()) {
             if ty.is_union()
-                && self.ctx.options().rust_features().untagged_union()
+                && self.ctx.options().rust_features().untagged_union
             {
                 trace!(
                     "    cannot derive `PartialEq`/`PartialOrd` for Rust unions"
@@ -242,7 +242,7 @@ impl<'ctx> CannotDerivePartialEqOrPartialOrd<'ctx> {
                 }
 
                 if info.kind() == CompKind::Union {
-                    if self.ctx.options().rust_features().untagged_union() {
+                    if self.ctx.options().rust_features().untagged_union {
                         trace!(
                             "    cannot derive `PartialEq`/`PartialOrd` for Rust unions"
                         );
diff --git a/src/ir/comp.rs b/src/ir/comp.rs
index 24909cb5..131851fd 100644
--- a/src/ir/comp.rs
+++ b/src/ir/comp.rs
@@ -1543,7 +1543,7 @@ impl CompInfo {
     ///     1. Current RustTarget allows for `untagged_union`
     ///     2. Each field can derive `Copy`
     pub fn can_be_rust_union(&self, ctx: &BindgenContext) -> bool {
-        if !ctx.options().rust_features().untagged_union() {
+        if !ctx.options().rust_features().untagged_union {
             return false;
         }
 
diff --git a/src/lib.rs b/src/lib.rs
index db58f6f4..6346ff80 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -600,6 +600,12 @@ impl Builder {
         self
     }
 
+    /// Disable support for native Rust unions, if supported.
+    pub fn disable_untagged_union(mut self) -> Self {
+        self.options.rust_features.untagged_union = false;
+        self
+    }
+
     /// Set the output graphviz file.
     pub fn emit_ir_graphviz<T: Into<String>>(mut self, path: T) -> Builder {
         let path = path.into();