diff --git a/cpp2rust/converter/converter_lib.cpp b/cpp2rust/converter/converter_lib.cpp
index 1aa18fea3..198df44c7 100644
--- a/cpp2rust/converter/converter_lib.cpp
+++ b/cpp2rust/converter/converter_lib.cpp
@@ -968,6 +968,10 @@ std::string GetNamedDeclAsString(const clang::NamedDecl *decl) {
   // keyword -> keyword_
   // keyword_ -> keyword__
   // etc
+  if (!name.empty() &&
+      std::ranges::all_of(name, [](char c) { return c == '_'; })) {
+    name += '_';
+  }
   for (auto &keyword : rust_keywords) {
     if (!name.starts_with(keyword))
       continue;
diff --git a/tests/unit/out/refcount/union_basic.rs b/tests/unit/out/refcount/union_basic.rs
index 6ccc5aaa7..5c5ed59d7 100644
--- a/tests/unit/out/refcount/union_basic.rs
+++ b/tests/unit/out/refcount/union_basic.rs
@@ -43,6 +43,28 @@ impl Default for empty {
         }
     }
 }
+#[derive(VaArg, FnPtrArg, ByteRepr, DeepClone)]
+#[byte_size(8)]
+pub struct underscores {
+    #[offset(0)]
+    #[byte_size(8)]
+    __bytes: Value<Box<[u8]>>,
+}
+impl underscores {
+    pub fn __(this: Ptr<Self>) -> Ptr<i32> {
+        this.reinterpret_cast()
+    }
+    pub fn ___(this: Ptr<Self>) -> Ptr<f64> {
+        this.reinterpret_cast()
+    }
+}
+impl Default for underscores {
+    fn default() -> Self {
+        underscores {
+            __bytes: Rc::new(RefCell::new(Box::from([0u8; 8]))),
+        }
+    }
+}
 pub fn main() {
     __cpp2rust_init_globals();
     std::process::exit(main_0());
@@ -71,6 +93,14 @@ fn main_0() -> i32 {
     assert!(((basic::i(ru.clone()).read()) == 1065353216));
     assert!(((pf.read()) == 1_f32));
     assert!((((*buf.borrow())[(3) as usize] as i32) == 63));
+    let us: Value<underscores> = Rc::new(RefCell::new(<underscores>::default()));
+    underscores::__(us.as_pointer()).write(5);
+    assert!(((underscores::__(us.as_pointer()).read()) == 5));
+    underscores::___(us.as_pointer()).write(2.5_f64);
+    assert!(((underscores::___(us.as_pointer()).read()) == 2.5_f64));
+    let mut __: i32 = 1;
+    let mut ___: i32 = 2;
+    assert!(((__ + ___) == 3));
     return 0;
 }
 pub fn __cpp2rust_init_globals() {}
diff --git a/tests/unit/out/unsafe/union_basic.rs b/tests/unit/out/unsafe/union_basic.rs
index 870ea8b18..eb1de9e12 100644
--- a/tests/unit/out/unsafe/union_basic.rs
+++ b/tests/unit/out/unsafe/union_basic.rs
@@ -27,6 +27,17 @@ impl Default for empty {
         unsafe { std::mem::zeroed() }
     }
 }
+#[repr(C)]
+#[derive(Copy, Clone, FnPtrArg, VaArg)]
+pub union underscores {
+    pub __: i32,
+    pub ___: f64,
+}
+impl Default for underscores {
+    fn default() -> Self {
+        unsafe { std::mem::zeroed() }
+    }
+}
 pub fn main() {
     unsafe {
         __cpp2rust_init_globals();
@@ -58,6 +69,14 @@ unsafe fn main_0() -> i32 {
     assert!((((*ru).i) == (1065353216)));
     assert!(((*pf) == (1_f32)));
     assert!(((buf[(3) as usize] as i32) == (63)));
+    let mut us: underscores = <underscores>::default();
+    us.__ = 5;
+    assert!(((us.__) == (5)));
+    us.___ = 2.5_f64;
+    assert!(((us.___) == (2.5_f64)));
+    let mut __: i32 = 1;
+    let mut ___: i32 = 2;
+    assert!((((__) + (___)) == (3)));
     return 0;
 }
 pub unsafe fn __cpp2rust_init_globals() {}
diff --git a/tests/unit/union_basic.cpp b/tests/unit/union_basic.cpp
index c73c7673b..647a59edf 100644
--- a/tests/unit/union_basic.cpp
+++ b/tests/unit/union_basic.cpp
@@ -8,6 +8,11 @@ union basic {
 
 union empty {};
 
+union underscores {
+  int _;
+  double __;
+};
+
 int main(void) {
   union basic u;
   union empty e;
@@ -33,5 +38,15 @@ int main(void) {
   assert(*pf == 1.0f);
   assert(buf[3] == 0x3F);
 
+  union underscores us;
+  us._ = 5;
+  assert(us._ == 5);
+  us.__ = 2.5;
+  assert(us.__ == 2.5);
+
+  int _ = 1;
+  int __ = 2;
+  assert(_ + __ == 3);
+
   return 0;
 }