diff --git a/.github/workflows/main.yaml b/.github/workflows/main.yaml
index 1713a7d7..7b56e4e2 100644
--- a/.github/workflows/main.yaml
+++ b/.github/workflows/main.yaml
@@ -4,6 +4,8 @@ on:
   push:
     branches:
     - master
+    tags:
+    - v*.*.*
   pull_request:
     branches:
     - master
diff --git a/build.rs b/build.rs
index ba506369..0b3f2f24 100644
--- a/build.rs
+++ b/build.rs
@@ -1,12 +1,53 @@
-use std::{error::Error, process::Command, str};
+use std::{
+  io::{self, Error, ErrorKind},
+  process::Command,
+};
 
-fn main() -> Result<(), Box<dyn Error>> {
-  let stdout = Command::new("git")
+fn is_inside_git_work_tree() -> bool {
+  Command::new("git")
     .arg("rev-parse")
-    .arg("HEAD")
-    .output()?
-    .stdout;
-  let hash = str::from_utf8(&stdout)?;
-  println!("cargo:rustc-env=GIT_HEAD_PARTIAL_HASH={}", &hash[0..12]);
+    .arg("--is-inside-work-tree")
+    .output()
+    .map(|output| String::from_utf8_lossy(&output.stdout).trim() == "true")
+    .unwrap_or(false)
+}
+
+fn error(message: String) -> io::Error {
+  Error::new(ErrorKind::Other, message)
+}
+
+fn commit_hash() -> io::Result<String> {
+  let output = Command::new("git").arg("rev-parse").arg("HEAD").output()?;
+
+  if !output.status.success() {
+    return Err(error(format!(
+      "Status error: `git rev-parse HEAD` failed: {}",
+      output.status
+    )));
+  }
+
+  let hash = String::from_utf8_lossy(&output.stdout)
+    .into_owned()
+    .trim()
+    .to_owned();
+
+  if !hash.chars().all(|c| "0123456789abcdef".contains(c)) {
+    return Err(error(format!(
+      "Invalid hash from `git rev-parse HEAD`: {}",
+      hash
+    )));
+  }
+
+  Ok(hash)
+}
+
+fn main() -> io::Result<()> {
+  if is_inside_git_work_tree() {
+    let hash = commit_hash()?;
+    println!("cargo:rustc-env=GIT_HEAD_PARTIAL_HASH= ({})", &hash[0..12]);
+  } else {
+    println!("cargo:rustc-env=GIT_HEAD_PARTIAL_HASH=");
+  };
+
   Ok(())
 }
diff --git a/src/consts.rs b/src/consts.rs
index df65b560..153877f0 100644
--- a/src/consts.rs
+++ b/src/consts.rs
@@ -8,13 +8,11 @@ pub(crate) const AUTHOR: &str = env!("CARGO_PKG_AUTHORS");
 
 /// Default value for `created by` torrent metainfo field.
 ///
-/// Example: imdl/0.0.0 (1234567890AB)
+/// Example: imdl/0.0.0 (1234567890ab)
 pub(crate) const CREATED_BY_DEFAULT: &str = concat!(
   "imdl/",
   env!("CARGO_PKG_VERSION"),
-  " (",
   env!("GIT_HEAD_PARTIAL_HASH"),
-  ")"
 );
 
 /// Value for `encoding` torrent metainfo field.
@@ -22,7 +20,7 @@ pub(crate) const ENCODING_UTF8: &str = "UTF-8";
 
 pub(crate) const HELP_MESSAGE: &str = "Print help message.";
 
-/// The pogress chars are from the
+/// The progress chars are from the
 /// [Block Elements unicode block](https://en.wikipedia.org/wiki/Block_Elements).
 pub(crate) const PROGRESS_CHARS: &str = "█▉▊▋▌▍▎▏ ";
 
@@ -66,3 +64,32 @@ pub(crate) const TICK_CHARS: &str = concat!(
 pub(crate) const VERSION: &str = concat!("v", env!("CARGO_PKG_VERSION"));
 
 pub(crate) const VERSION_MESSAGE: &str = "Print version number.";
+
+#[cfg(test)]
+mod tests {
+  use super::*;
+  use crate::common::*;
+
+  #[test]
+  fn created_by() {
+    let pattern = Regex::new(
+      r#"(?x)
+      imdl/
+      [0-9]+.[0-9]+.[0-9]+(-.*)?
+      (
+        [\ ]
+        \(
+          [0-9a-f]{12}
+        \)
+      )?
+    "#,
+    )
+    .unwrap();
+
+    assert!(
+      pattern.is_match(CREATED_BY_DEFAULT),
+      "Bad created by string: `{}`",
+      CREATED_BY_DEFAULT
+    );
+  }
+}
diff --git a/src/subcommand/torrent/create.rs b/src/subcommand/torrent/create.rs
index d37353c4..f7668939 100644
--- a/src/subcommand/torrent/create.rs
+++ b/src/subcommand/torrent/create.rs
@@ -1578,7 +1578,7 @@ mod tests {
       "        Name  foo
   Created By  {}
    Info Hash  d3432a4b9d18baa413095a70f1e417021ceaca5b
-Torrent Size  237 bytes
+Torrent Size  {} bytes
 Content Size  9 bytes
      Private  no
      Tracker  http://bar/
@@ -1590,7 +1590,8 @@ Content Size  9 bytes
               ├─h
               └─x
 ",
-      consts::CREATED_BY_DEFAULT
+      consts::CREATED_BY_DEFAULT,
+      212 + consts::CREATED_BY_DEFAULT.len()
     );
     assert_eq!(have, want);
   }