diff --git a/CHANGELOG.md b/CHANGELOG.md
index a73b91d2b..c203cdf5b 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -14,6 +14,7 @@
 - The `--parallel` unsupported-OS warning no longer claims Alpine is excluded: Alpine has been a supported parallel platform since the race conditions were fixed, the message was simply never updated
 
 ### Fixed
+- An unknown option is now rejected with a clear error and a non-zero exit instead of being silently filed under test paths. A mistyped flag used to degrade the run while still reporting success: `bashunit --parralel tests/` ran sequentially and exited `0`, and `bashunit --filterr foo tests/` swallowed both the flag and its value and ran the whole suite. Applies to `test` and `bench`; the `assert` subcommand parses its own arguments and is unchanged (#871)
 - The quickstart's sample output showed durations as `16 ms` / `90 ms`; bashunit prints `16ms` / `90ms`
 - `.env.example` documented `BASHUNIT_SHOW_EXECUTION_TIME` as defaulting to `true`; the actual default has been `auto` since #765
 - bashunit now aborts with an actionable error when its scratch directories under `TMPDIR` cannot be created. Previously the run continued with every failure/skip collector writing nowhere, so a failing suite still exited non-zero but lost its assertion detail and leaked raw `src/runner.sh: line N: ...: Not a directory` errors instead of reporting the cause
diff --git a/src/main.sh b/src/main.sh
index 7ab7f50db..c8cd4bc14 100644
--- a/src/main.sh
+++ b/src/main.sh
@@ -1,5 +1,15 @@
 #!/usr/bin/env bash
 
+##
+# Prints an "unknown option" error and exits non-zero.
+# Arguments: $1 - the offending argument, $2 - subcommand to name in the hint
+##
+function bashunit::main::abort_unknown_option() {
+  printf "%sError: unknown option '%s'. Run 'bashunit %s --help' to list the available options.%s\n" \
+    "${_BASHUNIT_COLOR_FAILED}" "$1" "$2" "${_BASHUNIT_COLOR_DEFAULT}" >&2
+  exit 1
+}
+
 ##
 # Validates a `--shard <index>/<total>` spec and exports the parts, or prints an
 # error and exits non-zero. Requires numeric index/total with 1 <= index <= total.
@@ -329,6 +339,13 @@ function bashunit::main::cmd_test() {
       fi
       _bashunit_coverage_opt_set=true
       ;;
+    -*)
+      # Anything option-shaped reaching here matched no branch above. It used to
+      # be filed under test paths, so a typo degraded the run silently and still
+      # exited 0: `--parralel` ran sequentially, `--filterr x` ran the whole
+      # suite (#871). Test paths never start with a dash.
+      bashunit::main::abort_unknown_option "$1" "test"
+      ;;
     *)
       raw_args[raw_args_count]="$1"
       raw_args_count=$((raw_args_count + 1))
@@ -529,6 +546,9 @@ function bashunit::main::cmd_bench() {
       bashunit::console_header::print_bench_help
       exit 0
       ;;
+    -*)
+      bashunit::main::abort_unknown_option "$1" "bench"
+      ;;
     *)
       raw_args[raw_args_count]="$1"
       raw_args_count=$((raw_args_count + 1))
diff --git a/tests/acceptance/bashunit_unknown_option_test.sh b/tests/acceptance/bashunit_unknown_option_test.sh
new file mode 100644
index 000000000..17ccf2d26
--- /dev/null
+++ b/tests/acceptance/bashunit_unknown_option_test.sh
@@ -0,0 +1,66 @@
+#!/usr/bin/env bash
+set -euo pipefail
+
+function set_up_before_script() {
+  TEST_ENV_FILE="tests/acceptance/fixtures/.env.default"
+  TEST_FILE="tests/acceptance/fixtures/tests_path/a_test.sh"
+}
+
+# An unmatched option used to fall through to the test-path list, so the run
+# continued with the flag silently ignored and still exited 0 (#871).
+function test_bashunit_fails_when_given_an_unknown_option() {
+  local ec=0
+  local output
+  output=$(./bashunit --env "$TEST_ENV_FILE" --parralel "$TEST_FILE" 2>&1) || ec=$?
+
+  assert_general_error "" "" "$ec"
+  assert_contains "--parralel" "$output"
+}
+
+function test_bashunit_reports_an_unknown_option_before_running_any_test() {
+  local output
+  output=$(./bashunit --env "$TEST_ENV_FILE" --parralel "$TEST_FILE" 2>&1 || true)
+
+  assert_not_contains "All tests passed" "$output"
+}
+
+# The value of a mistyped value-taking flag must not be mistaken for a test path.
+function test_bashunit_fails_when_given_an_unknown_option_that_takes_a_value() {
+  local ec=0
+  local output
+  output=$(./bashunit --env "$TEST_ENV_FILE" --filterr nope "$TEST_FILE" 2>&1) || ec=$?
+
+  assert_general_error "" "" "$ec"
+  assert_contains "--filterr" "$output"
+}
+
+function test_bashunit_still_accepts_a_known_option_with_a_path() {
+  local ec=0
+  local output
+  output=$(./bashunit --env "$TEST_ENV_FILE" --no-parallel "$TEST_FILE" 2>&1) || ec=$?
+
+  assert_successful_code "" "" "$ec"
+  assert_contains "All tests passed" "$output"
+}
+
+function test_bashunit_bench_fails_when_given_an_unknown_option() {
+  local bench_dir
+  bench_dir="$(bashunit::temp_dir)"
+  printf '#!/usr/bin/env bash\nfunction bench_sample() { :; }\n' >"$bench_dir/sample_bench.sh"
+
+  local ec=0
+  local output
+  output=$(./bashunit bench --nonsense-flag "$bench_dir" 2>&1) || ec=$?
+
+  assert_general_error "" "" "$ec"
+  assert_contains "--nonsense-flag" "$output"
+}
+
+function test_bashunit_still_accepts_a_bare_path() {
+  local ec=0
+  local output
+  output=$(./bashunit --env "$TEST_ENV_FILE" "$TEST_FILE" 2>&1) || ec=$?
+
+  assert_successful_code "" "" "$ec"
+  assert_contains "All tests passed" "$output"
+}