diff --git a/gen/src/include.rs b/gen/src/include.rs
index be0bd8e..0ed76ac 100644
--- a/gen/src/include.rs
+++ b/gen/src/include.rs
@@ -1,21 +1,42 @@
+use crate::gen::out::OutFile;
 use std::fmt::{self, Display};
 
 pub static HEADER: &str = include_str!("include/cxx.h");
 
-pub fn get(guard: &str) -> &'static str {
+pub(super) fn write(out: &mut OutFile, needed: bool, guard: &str) {
     let ifndef = format!("#ifndef {}", guard);
+    let define = format!("#define {}", guard);
     let endif = format!("#endif // {}", guard);
-    let begin = find_line(&ifndef);
-    let end = find_line(&endif);
-    if let (Some(begin), Some(end)) = (begin, end) {
-        &HEADER[begin..end + endif.len()]
-    } else {
-        panic!("not found in cxx.h header: {}", guard)
+
+    let mut offset = 0;
+    loop {
+        let begin = find_line(offset, &ifndef);
+        let end = find_line(offset, &endif);
+        if let (Some(begin), Some(end)) = (begin, end) {
+            if !needed {
+                return;
+            }
+            out.next_section();
+            if offset == 0 {
+                writeln!(out, "{}", ifndef);
+                writeln!(out, "{}", define);
+            }
+            for line in HEADER[begin + ifndef.len()..end].trim().lines() {
+                if line != define && !line.trim_start().starts_with("//") {
+                    writeln!(out, "{}", line);
+                }
+            }
+            offset = end + endif.len();
+        } else if offset == 0 {
+            panic!("not found in cxx.h header: {}", guard)
+        } else {
+            writeln!(out, "{}", endif);
+            return;
+        }
     }
 }
 
-fn find_line(line: &str) -> Option<usize> {
-    let mut offset = 0;
+fn find_line(mut offset: usize, line: &str) -> Option<usize> {
     loop {
         offset += HEADER[offset..].find(line)?;
         let rest = &HEADER[offset + line.len()..];
diff --git a/gen/src/write.rs b/gen/src/write.rs
index 12f2839..c06fce9 100644
--- a/gen/src/write.rs
+++ b/gen/src/write.rs
@@ -249,15 +249,15 @@
         writeln!(out, "struct unsafe_bitcopy_t;");
     }
 
-    write_header_section(out, needs_rust_string, "CXXBRIDGE03_RUST_STRING");
-    write_header_section(out, needs_rust_str, "CXXBRIDGE03_RUST_STR");
-    write_header_section(out, needs_rust_slice, "CXXBRIDGE03_RUST_SLICE");
-    write_header_section(out, needs_rust_box, "CXXBRIDGE03_RUST_BOX");
-    write_header_section(out, needs_rust_vec, "CXXBRIDGE03_RUST_VEC");
-    write_header_section(out, needs_rust_fn, "CXXBRIDGE03_RUST_FN");
-    write_header_section(out, needs_rust_error, "CXXBRIDGE03_RUST_ERROR");
-    write_header_section(out, needs_rust_isize, "CXXBRIDGE03_RUST_ISIZE");
-    write_header_section(out, needs_unsafe_bitcopy, "CXXBRIDGE03_RUST_BITCOPY");
+    include::write(out, needs_rust_string, "CXXBRIDGE03_RUST_STRING");
+    include::write(out, needs_rust_str, "CXXBRIDGE03_RUST_STR");
+    include::write(out, needs_rust_slice, "CXXBRIDGE03_RUST_SLICE");
+    include::write(out, needs_rust_box, "CXXBRIDGE03_RUST_BOX");
+    include::write(out, needs_rust_vec, "CXXBRIDGE03_RUST_VEC");
+    include::write(out, needs_rust_fn, "CXXBRIDGE03_RUST_FN");
+    include::write(out, needs_rust_error, "CXXBRIDGE03_RUST_ERROR");
+    include::write(out, needs_rust_isize, "CXXBRIDGE03_RUST_ISIZE");
+    include::write(out, needs_unsafe_bitcopy, "CXXBRIDGE03_RUST_BITCOPY");
 
     if needs_manually_drop {
         out.next_section();
@@ -311,18 +311,6 @@
     out.end_block("namespace rust");
 }
 
-fn write_header_section(out: &mut OutFile, needed: bool, section: &str) {
-    let section = include::get(section);
-    if needed {
-        out.next_section();
-        for line in section.lines() {
-            if !line.trim_start().starts_with("//") {
-                writeln!(out, "{}", line);
-            }
-        }
-    }
-}
-
 fn write_struct(out: &mut OutFile, strct: &Struct) {
     for line in strct.doc.to_string().lines() {
         writeln!(out, "//{}", line);