diff --git a/bindgen-tests/tests/expectations/tests/union_template_forward_decl.rs b/bindgen-tests/tests/expectations/tests/union_template_forward_decl.rs
new file mode 100644
index 0000000000..c934f49a8e
--- /dev/null
+++ b/bindgen-tests/tests/expectations/tests/union_template_forward_decl.rs
@@ -0,0 +1,27 @@
+#![allow(
+    dead_code,
+    non_snake_case,
+    non_camel_case_types,
+    non_upper_case_globals
+)]
+
+#[repr(C)]
+pub struct declare_union {
+    _unused: [u8; 0],
+}
+#[repr(C)]
+pub union define_union<value_t> {
+    pub value: *mut value_t,
+    pub dummy: ::std::os::raw::c_int,
+    pub _phantom_0:
+        ::std::marker::PhantomData<::std::cell::UnsafeCell<value_t>>,
+}
+impl<value_t> Default for define_union<value_t> {
+    fn default() -> Self {
+        let mut s = ::std::mem::MaybeUninit::<Self>::uninit();
+        unsafe {
+            ::std::ptr::write_bytes(s.as_mut_ptr(), 0, 1);
+            s.assume_init()
+        }
+    }
+}
diff --git a/bindgen-tests/tests/headers/union_template_forward_decl.hpp b/bindgen-tests/tests/headers/union_template_forward_decl.hpp
new file mode 100644
index 0000000000..4fb4bc5ad9
--- /dev/null
+++ b/bindgen-tests/tests/headers/union_template_forward_decl.hpp
@@ -0,0 +1,17 @@
+// bindgen-flags: --with-derive-hash --with-derive-partialeq --with-derive-eq
+//
+template <typename value_t>
+union declare_union; // Primary template declared, but never defined.
+
+template <typename value_t> union declare_union<value_t *> {
+  declare_union() {}
+  declare_union(value_t *a_value) : value(a_value) {}
+  value_t *value;
+};
+
+template <typename value_t> union define_union {
+  define_union() {}
+  define_union(value_t *a_value) : value(a_value) {}
+  value_t *value;
+  int dummy;
+};
diff --git a/bindgen/ir/comp.rs b/bindgen/ir/comp.rs
index 18a4291cf9..0bff3982ae 100644
--- a/bindgen/ir/comp.rs
+++ b/bindgen/ir/comp.rs
@@ -1275,6 +1275,7 @@ impl CompInfo {
                 CXCursor_ParmDecl => true,
                 CXCursor_StructDecl | CXCursor_UnionDecl |
                 CXCursor_ClassDecl => !cur.is_definition(),
+                CXCursor_ClassTemplate => kind == CompKind::Union && !cur.is_definition(), 
                 _ => false,
             });