diff --git a/CHANGELOG.md b/CHANGELOG.md
index 7f62c1e4..b1962715 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -2,6 +2,9 @@
 
 ## Unreleased
 
+### Added
+- `assert_file_permissions <mode> <file>` asserts a file's octal permission mode (`644`, `0755`); portable across GNU/BSD `stat` (#742)
+
 ### 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)
 
diff --git a/docs/assertions.md b/docs/assertions.md
index 73194ff8..39a42817 100644
--- a/docs/assertions.md
+++ b/docs/assertions.md
@@ -830,6 +830,33 @@ function test_failure() {
 ```
 :::
 
+## assert_file_permissions
+> `assert_file_permissions "mode" "file"`
+
+Reports an error if `file` does not have the expected octal permission `mode`
+(e.g. `644`, `0755`). A leading zero is optional (`0755` and `755` are equal).
+Works on both Linux (GNU `stat`) and macOS (BSD `stat`).
+
+::: code-group
+```bash [Example]
+function test_success() {
+  local file="/tmp/file-path.txt"
+  touch "$file"
+  chmod 600 "$file"
+
+  assert_file_permissions "600" "$file"
+}
+
+function test_failure() {
+  local file="/tmp/file-path.txt"
+  touch "$file"
+  chmod 644 "$file"
+
+  assert_file_permissions "600" "$file"
+}
+```
+:::
+
 ## assert_is_file
 > `assert_is_file "file"`
 
diff --git a/src/assert_files.sh b/src/assert_files.sh
index 27fab431..aeca0048 100644
--- a/src/assert_files.sh
+++ b/src/assert_files.sh
@@ -149,3 +149,54 @@ function assert_file_not_contains() {
 
   bashunit::state::add_assertions_passed
 }
+
+##
+# Normalizes an octal file mode to its decimal value, dropping leading zeros
+# (so "0755" and "755" compare equal). Echoes nothing on invalid octal input.
+# Arguments: $1 - octal mode string
+##
+function bashunit::assert::_octal_to_decimal() {
+  local mode="$1"
+  case "$mode" in
+  '' | *[!0-7]*) return 1 ;;
+  esac
+  printf '%d' "$((8#$mode))"
+}
+
+##
+# Asserts a file has the expected octal permission mode (e.g. "644", "0755").
+# Arguments: $1 - expected octal mode, $2 - file path
+##
+function assert_file_permissions() {
+  bashunit::assert::should_skip && return 0
+
+  local expected="$1"
+  local file="$2"
+  local test_fn
+  test_fn="$(bashunit::helper::find_test_function_name)"
+  local label
+  label="$(bashunit::helper::normalize_test_function_name "$test_fn")"
+
+  if [ ! -e "$file" ]; then
+    bashunit::assert::mark_failed
+    bashunit::console_results::print_failed_test \
+      "${label}" "${file}" "to have permissions ${expected}" "but the file does not exist"
+    return
+  fi
+
+  local actual
+  actual="$(stat -c '%a' "$file" 2>/dev/null || stat -f '%Lp' "$file" 2>/dev/null)"
+
+  local expected_dec actual_dec
+  expected_dec="$(bashunit::assert::_octal_to_decimal "$expected")"
+  actual_dec="$(bashunit::assert::_octal_to_decimal "$actual")"
+
+  if [ "$expected_dec" != "$actual_dec" ]; then
+    bashunit::assert::mark_failed
+    bashunit::console_results::print_failed_test \
+      "${label}" "${file}" "to have permissions ${expected}" "but got ${actual}"
+    return
+  fi
+
+  bashunit::state::add_assertions_passed
+}
diff --git a/tests/acceptance/snapshots/bashunit_test_sh.test_bashunit_should_display_all_assert_docs.snapshot b/tests/acceptance/snapshots/bashunit_test_sh.test_bashunit_should_display_all_assert_docs.snapshot
index e8232e44..3657a9d4 100644
--- a/tests/acceptance/snapshots/bashunit_test_sh.test_bashunit_should_display_all_assert_docs.snapshot
+++ b/tests/acceptance/snapshots/bashunit_test_sh.test_bashunit_should_display_all_assert_docs.snapshot
@@ -340,6 +340,15 @@ Reports an error if `file` does not contains the search string.
 - assert_file_not_contains is the inverse of this assertion and takes the same arguments.
 
 
+## assert_file_permissions
+--------------
+> `assert_file_permissions "mode" "file"`
+
+Reports an error if `file` does not have the expected octal permission `mode`
+(e.g. `644`, `0755`). A leading zero is optional (`0755` and `755` are equal).
+Works on both Linux (GNU `stat`) and macOS (BSD `stat`).
+
+
 ## assert_is_file
 --------------
 > `assert_is_file "file"`
@@ -589,3 +598,5 @@ Reports an error if `command` completes in `threshold_ms` milliseconds or less.
 
 Unambiguously reports an error message. Useful for reporting specific message
 when testing situations not covered by any `assert_*` functions.
+
+
diff --git a/tests/unit/file_test.sh b/tests/unit/file_test.sh
index 848b5686..9fc424af 100644
--- a/tests/unit/file_test.sh
+++ b/tests/unit/file_test.sh
@@ -190,3 +190,62 @@ function test_fails_assert_file_not_contains() {
 
   rm "$file"
 }
+
+# shellcheck disable=SC2155
+function test_successful_assert_file_permissions() {
+  # Windows (Git Bash) fakes POSIX permissions, so chmod/stat are unreliable there.
+  if bashunit::check_os::is_windows; then
+    bashunit::skip && return
+  fi
+
+  local file="/tmp/test_successful_assert_file_permissions_$$"
+  touch "$file"
+  chmod 600 "$file"
+
+  assert_empty "$(assert_file_permissions "600" "$file")"
+
+  rm "$file"
+}
+
+# shellcheck disable=SC2155
+function test_successful_assert_file_permissions_accepts_leading_zero() {
+  if bashunit::check_os::is_windows; then
+    bashunit::skip && return
+  fi
+
+  local file="/tmp/test_assert_file_permissions_leading_zero_$$"
+  touch "$file"
+  chmod 755 "$file"
+
+  assert_empty "$(assert_file_permissions "0755" "$file")"
+
+  rm "$file"
+}
+
+# shellcheck disable=SC2155
+function test_unsuccessful_assert_file_permissions() {
+  if bashunit::check_os::is_windows; then
+    bashunit::skip && return
+  fi
+
+  local file="/tmp/test_unsuccessful_assert_file_permissions_$$"
+  touch "$file"
+  chmod 600 "$file"
+
+  assert_same \
+    "$(bashunit::console_results::print_failed_test \
+    "Unsuccessful assert file permissions" "$file" "to have permissions 644" "but got 600")" \
+    "$(assert_file_permissions "644" "$file")"
+
+  rm "$file"
+}
+
+function test_unsuccessful_assert_file_permissions_when_file_does_not_exist() {
+  local file="a_random_file_that_will_not_exist"
+
+  assert_same \
+    "$(bashunit::console_results::print_failed_test \
+    "Unsuccessful assert file permissions when file does not exist" \
+    "$file" "to have permissions 644" "but the file does not exist")" \
+    "$(assert_file_permissions "644" "$file")"
+}