diff --git a/generate/src/main.rs b/generate/src/main.rs
index e56976a..5fdaaa6 100644
--- a/generate/src/main.rs
+++ b/generate/src/main.rs
@@ -110,7 +110,7 @@ fn write_emojis_slice<W: io::Write>(
 }
 
 fn write_phf_map<W: io::Write>(w: &mut W, map: HashMap<String, String>) -> Result<()> {
-    write!(w, "pub static MAP: phf::Map<&'static str, usize> = ")?;
+    write!(w, "pub static MAP: ::phf::Map<&'static str, usize> = ")?;
     let mut gen = phf_codegen::Map::new();
     for (key, value) in &map {
         gen.entry(key, value);
@@ -119,6 +119,8 @@ fn write_phf_map<W: io::Write>(w: &mut W, map: HashMap<String, String>) -> Resul
     Ok(())
 }
 
+const HEADER: &str = "// Code generated by `cargo run --package generate`. DO NOT EDIT.\n";
+
 fn main() -> Result<()> {
     let dir: PathBuf = [env!("CARGO_MANIFEST_DIR"), "..", "src", "gen"]
         .iter()
@@ -133,6 +135,7 @@ fn main() -> Result<()> {
     fs::create_dir_all(&dir)?;
 
     let mut f = fs::File::create(dir.join("mod.rs"))?;
+    writeln!(f, "{}", HEADER)?;
     writeln!(f, "#![cfg_attr(rustfmt, rustfmt::skip)]\n")?;
     writeln!(f, "pub mod shortcode;")?;
     writeln!(f, "pub mod unicode;\n")?;
@@ -149,9 +152,11 @@ fn main() -> Result<()> {
     )?;
 
     let mut f = fs::File::create(dir.join("unicode.rs"))?;
+    writeln!(f, "{}", HEADER)?;
     write_phf_map(&mut f, unicode_map)?;
 
     let mut f = fs::File::create(dir.join("shortcode.rs"))?;
+    writeln!(f, "{}", HEADER)?;
     write_phf_map(&mut f, shortcode_map)?;
 
     Ok(())
diff --git a/src/gen/mod.rs b/src/gen/mod.rs
index 744030e..3445901 100644
--- a/src/gen/mod.rs
+++ b/src/gen/mod.rs
@@ -1,3 +1,5 @@
+// Code generated by `cargo run --package generate`. DO NOT EDIT.
+
 #![cfg_attr(rustfmt, rustfmt::skip)]
 
 pub mod shortcode;
diff --git a/src/gen/shortcode.rs b/src/gen/shortcode.rs
index ca9cfb2..b297e61 100644
--- a/src/gen/shortcode.rs
+++ b/src/gen/shortcode.rs
@@ -1,4 +1,6 @@
-pub static MAP: phf::Map<&'static str, usize> = ::phf::Map {
+// Code generated by `cargo run --package generate`. DO NOT EDIT.
+
+pub static MAP: ::phf::Map<&'static str, usize> = ::phf::Map {
     key: 12913932095322966823,
     disps: &[
         (0, 627),
diff --git a/src/gen/unicode.rs b/src/gen/unicode.rs
index 64dbd7f..019e471 100644
--- a/src/gen/unicode.rs
+++ b/src/gen/unicode.rs
@@ -1,4 +1,6 @@
-pub static MAP: phf::Map<&'static str, usize> = ::phf::Map {
+// Code generated by `cargo run --package generate`. DO NOT EDIT.
+
+pub static MAP: ::phf::Map<&'static str, usize> = ::phf::Map {
     key: 12913932095322966823,
     disps: &[
         (0, 50),