diff --git a/CHANGELOG.md b/CHANGELOG.md
index 23bb8f7b..7f62c1e4 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -2,6 +2,9 @@
 
 ## Unreleased
 
+### Fixed
+- `watch` subcommand failed with `bashunit::watch::run: command not found` in the released binary because `src/watch.sh` was missing from the build; it is now bundled (#735)
+
 ### Changed
 - Faster test execution by removing subprocess forks from hot paths (no behaviour change)
 
diff --git a/build.sh b/build.sh
index 6963c94a..b622f331 100755
--- a/build.sh
+++ b/build.sh
@@ -107,6 +107,7 @@ function build::dependencies() {
     "src/helpers.sh"
     "src/test_title.sh"
     "src/upgrade.sh"
+    "src/watch.sh"
     "src/assertions.sh"
     "src/reports.sh"
     "src/runner.sh"
diff --git a/tests/unit/build_test.sh b/tests/unit/build_test.sh
new file mode 100644
index 00000000..8c52416e
--- /dev/null
+++ b/tests/unit/build_test.sh
@@ -0,0 +1,36 @@
+#!/usr/bin/env bash
+
+ROOT_DIR=""
+
+function set_up_before_script() {
+  ROOT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")/../.." && pwd)"
+}
+
+function src_files_sourced_by_entrypoint() {
+  # Dev-only helpers under src/dev/ are intentionally excluded from the build.
+  grep -oE 'src/[a-zA-Z0-9_/]+\.sh' "$ROOT_DIR/bashunit" | grep -v '^src/dev/' | sort -u
+}
+
+function src_files_in_build() {
+  grep -oE 'src/[a-zA-Z0-9_/]+\.sh' "$ROOT_DIR/build.sh" | sort -u
+}
+
+# Every src file the dev entrypoint sources (except dev-only helpers) must also be
+# bundled by build.sh, otherwise its functions are missing from the distributable
+# single-file binary (regressions: bench #0.31.0, watch #735).
+function test_build_bundles_every_src_file_sourced_by_entrypoint() {
+  local missing
+  missing=$(comm -23 <(src_files_sourced_by_entrypoint) <(src_files_in_build))
+
+  assert_empty "$missing"
+}
+
+function test_built_binary_defines_watch_run() {
+  local build_dir
+  build_dir=$(bashunit::temp_dir)
+
+  (cd "$ROOT_DIR" && bash build.sh "$build_dir") >/dev/null 2>&1
+
+  assert_file_exists "$build_dir/bashunit"
+  assert_equals "1" "$(grep -c 'function bashunit::watch::run()' "$build_dir/bashunit")"
+}