diff --git a/CHANGELOG.md b/CHANGELOG.md
index 4d844cf3..5fb61f9c 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -5,7 +5,7 @@
 ### Fixed
 - A failing `set_up_before_script`/`set_up` is now reported consistently: previously the same failure could be attributed (plain failing command), silently ignored (failing `cmd && var=x` guard on Bash 3.2 — the hook's real exit status was discarded), or silently counted with an off-by-one total and no message (Bash ≥ 4, where the ERR trap re-fired in the runner's scope). Every test in the affected file is now marked failed with the hook message, totals match the declared count, and the suite continues — a strict test file can no longer abort the whole run mid-suite via its top-level `set -euo pipefail` (#836)
 - `bashunit::env::is_diff_enabled` and `bashunit::cleanup_testcase_temp_files` no longer break callers under `set -u`/`set -e` (unbound read after `unset BASHUNIT_NO_DIFF`; skip path returned 1) (#836)
-- `--stop-on-failure`, `--log-junit`, `--report-html`, `--report-tap` and `--report-json` no longer leak into nested bashunit runs via the environment: a script under test that itself calls bashunit used to inherit the parent's stop-on-failure mode (aborting before the rerun cache was written) and overwrite the parent's report files (#834)
+- No run-mode flag leaks into nested bashunit runs via the environment anymore: after #834 fixed five flags, the remaining ~40 (`--parallel`, `--simple`, `--strict`, `--filter`, `--retry`, `--seed`, `--watch`, …) are now also this-process-only, so a script under test that itself calls bashunit gets default behavior instead of silently inheriting the parent's output mode, strictness, parallelism, timeouts or report paths. Env-var configuration (`BASHUNIT_*=… bashunit`) is unchanged (#834, #837)
 - `./bashunit bench` works again when running from a repository checkout: the dev entrypoint never sourced `src/benchmark.sh`, so every bench run crashed with `command not found` (the built binary was unaffected) (#834)
 - `./build.sh --verify` now exits non-zero when the built binary fails the test suite — previously a red verification run still reported success to CI. The gate exposed that verification had been silently crashing mid-suite since 2025-06: six test files resolved repo paths through the running binary's root dir, which has no `src/` in a build folder; they now resolve paths relative to the test file or repo cwd (#834)
 - Snapshot placeholders (`::ignore::`) now work on systems without perl; multi-line placeholders still need perl (#823)
diff --git a/bashunit b/bashunit
index 08763508..0ceb3391 100755
--- a/bashunit
+++ b/bashunit
@@ -42,10 +42,13 @@ export BASHUNIT_WORKING_DIR
 for arg in "$@"; do
   case "$arg" in
   --skip-env-file)
-    export BASHUNIT_SKIP_ENV_FILE=true
+    # this-process-only (see the flag-parse loop in src/main.sh) (#837)
+    BASHUNIT_SKIP_ENV_FILE=true
+    export -n BASHUNIT_SKIP_ENV_FILE
     ;;
   -l | --login)
-    export BASHUNIT_LOGIN_SHELL=true
+    BASHUNIT_LOGIN_SHELL=true
+    export -n BASHUNIT_LOGIN_SHELL
     ;;
   --no-color)
     # shellcheck disable=SC2034
diff --git a/src/main.sh b/src/main.sh
index 35de23cb..cf0c5b24 100644
--- a/src/main.sh
+++ b/src/main.sh
@@ -27,8 +27,10 @@ function bashunit::main::set_shard_or_exit() {
     exit 1
   fi
 
-  export BASHUNIT_SHARD_INDEX="$index"
-  export BASHUNIT_SHARD_TOTAL="$total"
+  BASHUNIT_SHARD_INDEX="$index"
+  export -n BASHUNIT_SHARD_INDEX
+  BASHUNIT_SHARD_TOTAL="$total"
+  export -n BASHUNIT_SHARD_TOTAL
 }
 
 #############################
@@ -46,7 +48,18 @@ function bashunit::main::cmd_test() {
   local assert_fn=""
   local _bashunit_coverage_opt_set=false
 
-  # Parse test-specific options
+  # Parse test-specific options.
+  #
+  # Flag branches assign WITHOUT export and strip the export attribute with
+  # `export -n`: run-mode flags are this-process-only. Everything that reads
+  # them (runner, reporters, parallel workers) runs in this shell or its
+  # subshells, which inherit unexported variables — while exec'd children
+  # (nested bashunit runs: bashunit's own acceptance suite under
+  # `build.sh --verify`, or a user's script under test that calls bashunit)
+  # must NOT inherit the parent's flags (#834, #837). The explicit `export -n`
+  # also clears an export attribute stamped by an allexport .env load.
+  # Pair any newly exported-by-necessity flag with a comment naming the exec'd
+  # consumer, and extend tests/acceptance/fixtures/flag_env_leak/leak_probe.sh.
   while [ $# -gt 0 ]; do
     case "$1" in
     -a | --assert)
@@ -74,13 +87,16 @@ function bashunit::main::cmd_test() {
       shift
       ;;
     -s | --simple)
-      export BASHUNIT_SIMPLE_OUTPUT=true
+      BASHUNIT_SIMPLE_OUTPUT=true
+      export -n BASHUNIT_SIMPLE_OUTPUT
       ;;
     --detailed)
-      export BASHUNIT_SIMPLE_OUTPUT=false
+      BASHUNIT_SIMPLE_OUTPUT=false
+      export -n BASHUNIT_SIMPLE_OUTPUT
       ;;
     --output)
-      export BASHUNIT_OUTPUT_FORMAT="$2"
+      BASHUNIT_OUTPUT_FORMAT="$2"
+      export -n BASHUNIT_OUTPUT_FORMAT
       shift
       ;;
     --debug)
@@ -101,35 +117,44 @@ function bashunit::main::cmd_test() {
       export -n BASHUNIT_STOP_ON_FAILURE
       ;;
     -p | --parallel)
-      export BASHUNIT_PARALLEL_RUN=true
+      BASHUNIT_PARALLEL_RUN=true
+      export -n BASHUNIT_PARALLEL_RUN
       ;;
     -j | --jobs)
-      export BASHUNIT_PARALLEL_RUN=true
+      BASHUNIT_PARALLEL_RUN=true
+      export -n BASHUNIT_PARALLEL_RUN
       # "auto" caps at the detected core count; wait_for_job_slot needs an
       # integer, so resolve it here rather than leaking the string downstream.
       if [ "$2" = "auto" ]; then
-        export BASHUNIT_PARALLEL_JOBS="$(bashunit::check_os::nproc)"
+        BASHUNIT_PARALLEL_JOBS="$(bashunit::check_os::nproc)"
+        export -n BASHUNIT_PARALLEL_JOBS
       else
-        export BASHUNIT_PARALLEL_JOBS="$2"
+        BASHUNIT_PARALLEL_JOBS="$2"
+        export -n BASHUNIT_PARALLEL_JOBS
       fi
       shift
       ;;
     --no-parallel)
-      export BASHUNIT_PARALLEL_RUN=false
+      BASHUNIT_PARALLEL_RUN=false
+      export -n BASHUNIT_PARALLEL_RUN
       ;;
     --test-timeout)
-      export BASHUNIT_TEST_TIMEOUT="$2"
+      BASHUNIT_TEST_TIMEOUT="$2"
+      export -n BASHUNIT_TEST_TIMEOUT
       shift
       ;;
     --retry)
-      export BASHUNIT_RETRY="$2"
+      BASHUNIT_RETRY="$2"
+      export -n BASHUNIT_RETRY
       shift
       ;;
     --random-order)
-      export BASHUNIT_RANDOM_ORDER=true
+      BASHUNIT_RANDOM_ORDER=true
+      export -n BASHUNIT_RANDOM_ORDER
       ;;
     --seed)
-      export BASHUNIT_SEED="$2"
+      BASHUNIT_SEED="$2"
+      export -n BASHUNIT_SEED
       shift
       ;;
     --shard)
@@ -137,17 +162,20 @@ function bashunit::main::cmd_test() {
       shift
       ;;
     --rerun-failed)
-      export BASHUNIT_RERUN_FAILED=true
+      BASHUNIT_RERUN_FAILED=true
+      export -n BASHUNIT_RERUN_FAILED
       ;;
     -w | --watch)
-      export BASHUNIT_WATCH_MODE=true
+      BASHUNIT_WATCH_MODE=true
+      export -n BASHUNIT_WATCH_MODE
       ;;
     -e | --env | --boot)
       # Support: --env "bootstrap.sh arg1 arg2"
       local boot_file="${2%% *}"
       local boot_args="${2#* }"
       if [ "$boot_args" != "$2" ]; then
-        export BASHUNIT_BOOTSTRAP_ARGS="$boot_args"
+        BASHUNIT_BOOTSTRAP_ARGS="$boot_args"
+        export -n BASHUNIT_BOOTSTRAP_ARGS
       fi
       # Export all variables from the env file so they're available in subshells
       # (e.g., process substitution used in load_test_files)
@@ -169,7 +197,8 @@ function bashunit::main::cmd_test() {
       shift
       ;;
     --log-gha)
-      export BASHUNIT_LOG_GHA="$2"
+      BASHUNIT_LOG_GHA="$2"
+      export -n BASHUNIT_LOG_GHA
       shift
       ;;
     -r | --report-html)
@@ -188,50 +217,64 @@ function bashunit::main::cmd_test() {
       shift
       ;;
     --no-output)
-      export BASHUNIT_NO_OUTPUT=true
+      BASHUNIT_NO_OUTPUT=true
+      export -n BASHUNIT_NO_OUTPUT
       ;;
     -vvv | --verbose)
-      export BASHUNIT_VERBOSE=true
+      BASHUNIT_VERBOSE=true
+      export -n BASHUNIT_VERBOSE
       ;;
     -h | --help)
       bashunit::console_header::print_test_help
       exit 0
       ;;
     --show-skipped)
-      export BASHUNIT_SHOW_SKIPPED=true
+      BASHUNIT_SHOW_SKIPPED=true
+      export -n BASHUNIT_SHOW_SKIPPED
       ;;
     --show-incomplete)
-      export BASHUNIT_SHOW_INCOMPLETE=true
+      BASHUNIT_SHOW_INCOMPLETE=true
+      export -n BASHUNIT_SHOW_INCOMPLETE
       ;;
     --failures-only)
-      export BASHUNIT_FAILURES_ONLY=true
+      BASHUNIT_FAILURES_ONLY=true
+      export -n BASHUNIT_FAILURES_ONLY
       ;;
     --fail-on-risky)
-      export BASHUNIT_FAIL_ON_RISKY=true
+      BASHUNIT_FAIL_ON_RISKY=true
+      export -n BASHUNIT_FAIL_ON_RISKY
       ;;
     --profile)
-      export BASHUNIT_PROFILE=true
+      BASHUNIT_PROFILE=true
+      export -n BASHUNIT_PROFILE
       ;;
     --show-output)
-      export BASHUNIT_SHOW_OUTPUT_ON_FAILURE=true
+      BASHUNIT_SHOW_OUTPUT_ON_FAILURE=true
+      export -n BASHUNIT_SHOW_OUTPUT_ON_FAILURE
       ;;
     --no-output-on-failure)
-      export BASHUNIT_SHOW_OUTPUT_ON_FAILURE=false
+      BASHUNIT_SHOW_OUTPUT_ON_FAILURE=false
+      export -n BASHUNIT_SHOW_OUTPUT_ON_FAILURE
       ;;
     --no-progress)
-      export BASHUNIT_NO_PROGRESS=true
+      BASHUNIT_NO_PROGRESS=true
+      export -n BASHUNIT_NO_PROGRESS
       ;;
     --strict)
-      export BASHUNIT_STRICT_MODE=true
+      BASHUNIT_STRICT_MODE=true
+      export -n BASHUNIT_STRICT_MODE
       ;;
     -R | --run-all)
-      export BASHUNIT_STOP_ON_ASSERTION_FAILURE=false
+      BASHUNIT_STOP_ON_ASSERTION_FAILURE=false
+      export -n BASHUNIT_STOP_ON_ASSERTION_FAILURE
       ;;
     --skip-env-file)
-      export BASHUNIT_SKIP_ENV_FILE=true
+      BASHUNIT_SKIP_ENV_FILE=true
+      export -n BASHUNIT_SKIP_ENV_FILE
       ;;
     -l | --login)
-      export BASHUNIT_LOGIN_SHELL=true
+      BASHUNIT_LOGIN_SHELL=true
+      export -n BASHUNIT_LOGIN_SHELL
       ;;
     --no-color)
       # shellcheck disable=SC2034
@@ -400,7 +443,8 @@ function bashunit::main::cmd_test() {
     # Disable coverage for assert mode - it's meant for running single assertions,
     # not tracking code coverage. This also prevents issues when parent bashunit
     # runs with coverage and calls subprocess bashunit with -a flag.
-    export BASHUNIT_COVERAGE=false
+    BASHUNIT_COVERAGE=false
+    export -n BASHUNIT_COVERAGE
     bashunit::main::exec_assert "$assert_fn" ${args+"${args[@]}"}
   else
     if [ "${BASHUNIT_WATCH_MODE:-false}" = true ]; then
@@ -431,7 +475,8 @@ function bashunit::main::cmd_bench() {
   local -a args=()
   local args_count=0
 
-  export BASHUNIT_BENCH_MODE=true
+  BASHUNIT_BENCH_MODE=true
+  export -n BASHUNIT_BENCH_MODE
 
   # Parse bench-specific options
   while [ $# -gt 0 ]; do
@@ -441,17 +486,20 @@ function bashunit::main::cmd_bench() {
       shift
       ;;
     -s | --simple)
-      export BASHUNIT_SIMPLE_OUTPUT=true
+      BASHUNIT_SIMPLE_OUTPUT=true
+      export -n BASHUNIT_SIMPLE_OUTPUT
       ;;
     --detailed)
-      export BASHUNIT_SIMPLE_OUTPUT=false
+      BASHUNIT_SIMPLE_OUTPUT=false
+      export -n BASHUNIT_SIMPLE_OUTPUT
       ;;
     -e | --env | --boot)
       # Support: --env "bootstrap.sh arg1 arg2"
       local boot_file="${2%% *}"
       local boot_args="${2#* }"
       if [ "$boot_args" != "$2" ]; then
-        export BASHUNIT_BOOTSTRAP_ARGS="$boot_args"
+        BASHUNIT_BOOTSTRAP_ARGS="$boot_args"
+        export -n BASHUNIT_BOOTSTRAP_ARGS
       fi
       # Export all variables from the env file so they're available in subshells
       # (e.g., process substitution used in load_test_files)
@@ -462,13 +510,16 @@ function bashunit::main::cmd_bench() {
       shift
       ;;
     -vvv | --verbose)
-      export BASHUNIT_VERBOSE=true
+      BASHUNIT_VERBOSE=true
+      export -n BASHUNIT_VERBOSE
       ;;
     --skip-env-file)
-      export BASHUNIT_SKIP_ENV_FILE=true
+      BASHUNIT_SKIP_ENV_FILE=true
+      export -n BASHUNIT_SKIP_ENV_FILE
       ;;
     -l | --login)
-      export BASHUNIT_LOGIN_SHELL=true
+      BASHUNIT_LOGIN_SHELL=true
+      export -n BASHUNIT_LOGIN_SHELL
       ;;
     --no-color)
       # shellcheck disable=SC2034
@@ -819,7 +870,8 @@ function bashunit::main::exec_tests() {
   # for replay and inherited by parallel test-file subshells.
   if bashunit::env::is_random_order_enabled; then
     if [ -z "${BASHUNIT_SEED:-}" ]; then
-      export BASHUNIT_SEED=$RANDOM
+      BASHUNIT_SEED=$RANDOM
+      export -n BASHUNIT_SEED
     fi
     if ! bashunit::env::is_tap_output_enabled; then
       bashunit::console_header::print_random_order_seed "$BASHUNIT_SEED"
diff --git a/tests/acceptance/bashunit_flag_env_leak_test.sh b/tests/acceptance/bashunit_flag_env_leak_test.sh
index 480984a2..c0607bc8 100644
--- a/tests/acceptance/bashunit_flag_env_leak_test.sh
+++ b/tests/acceptance/bashunit_flag_env_leak_test.sh
@@ -1,20 +1,26 @@
 #!/usr/bin/env bash
 set -euo pipefail
 
-# Regression guard for #834. Run-mode flags (--stop-on-failure and the report
-# writers) used to be exported, so nested bashunit runs — bashunit's own
-# acceptance tests under `build.sh --verify`, or a user's scripts under test
-# that call bashunit — inherited them: nested runs aborted before persisting
-# the rerun cache, wrote their own reports over the parent's files, and blew
-# the per-run fork budget.
+# Regression guard for #834/#837. Run-mode flags used to be exported, so nested
+# bashunit runs — bashunit's own acceptance tests under `build.sh --verify`, or
+# a user's scripts under test that call bashunit — inherited them: nested runs
+# aborted before persisting the rerun cache, wrote their own reports over the
+# parent's files, silently switched output/strict/parallel modes, and blew the
+# per-run fork budget. Every flag the parent sets here must be paired with a
+# name in leak_probe.sh's grep list (and vice versa).
 function test_run_mode_flags_do_not_leak_into_nested_runs() {
   local dir
   dir=$(bashunit::temp_dir)
 
   local output
   local exit_code=0
-  output=$(./bashunit --no-parallel --skip-env-file \
+  output=$(./bashunit --no-parallel --simple --strict --skip-env-file \
     --stop-on-failure \
+    --retry 1 \
+    --test-timeout 60 \
+    --random-order --seed 7 \
+    --no-progress \
+    --fail-on-risky \
     --log-junit "$dir/log-junit.xml" \
     --report-html "$dir/report.html" \
     --report-tap "$dir/report.tap" \
diff --git a/tests/acceptance/fixtures/flag_env_leak/leak_probe.sh b/tests/acceptance/fixtures/flag_env_leak/leak_probe.sh
index baaadbb3..1e1c6545 100644
--- a/tests/acceptance/fixtures/flag_env_leak/leak_probe.sh
+++ b/tests/acceptance/fixtures/flag_env_leak/leak_probe.sh
@@ -2,9 +2,16 @@
 
 # Probe used by bashunit_flag_env_leak_test.sh: fails if any run-mode flag of
 # the parent bashunit process leaked into this (nested) run's environment.
+# Every name listed here must be paired with the matching flag in the parent
+# invocation: the flag branch's `export -n` is also what clears an export
+# attribute stamped by an allexport .env load further up the process tree.
 function test_run_mode_flags_are_not_in_the_environment() {
+  local flags='STOP_ON_FAILURE|LOG_JUNIT|REPORT_HTML|REPORT_TAP|REPORT_JSON'
+  flags="$flags|PARALLEL_RUN|SIMPLE_OUTPUT|STRICT_MODE|RETRY|TEST_TIMEOUT"
+  flags="$flags|RANDOM_ORDER|SEED|NO_PROGRESS|FAIL_ON_RISKY|SKIP_ENV_FILE"
+
   local leaked
-  leaked="$(env | grep -E '^BASHUNIT_(STOP_ON_FAILURE|LOG_JUNIT|REPORT_HTML|REPORT_TAP|REPORT_JSON)=' || true)"
+  leaked="$(env | grep -E "^BASHUNIT_($flags)=" || true)"
 
   assert_empty "$leaked"
 }