diff --git a/bash-preexec.sh b/bash-preexec.sh
index b998944..6c88341 100644
--- a/bash-preexec.sh
+++ b/bash-preexec.sh
@@ -47,6 +47,12 @@ if [[ -z "${BASH_VERSINFO-}" ]] || (( BASH_VERSINFO[0] < 3 || (BASH_VERSINFO[0]
     return 1
 fi
 
+# We do not enable bash-preexc in non-interactive shells (except in tests).
+# `__bp_inside_test` is set in test/*.bats in bash-preexec repository.
+if [[ $- != *i* && ! ${__bp_inside_test-} ]]; then
+   return 0
+fi
+
 # Avoid duplicate inclusion
 if [[ -n "${bash_preexec_imported:-}" || -n "${__bp_imported:-}" ]]; then
     return 0
diff --git a/test/README.md b/test/README.md
index fd6613c..8836815 100644
--- a/test/README.md
+++ b/test/README.md
@@ -1,7 +1,7 @@
 Testing `bash-preexec`
 ======================
 
-**Note on test conditions**
+### Note on test conditions
 
 When writing test conditions, use `[ ... ]` instead of `[[ ... ]]` since the
 former are supported by Bats on Bash versions before 4.1. In particular, macOS
@@ -20,3 +20,14 @@ References:
 * [Differences between `[` and `[[`](http://mywiki.wooledge.org/BashFAQ/031)
 * [Problems with `[[` in Bats](https://github.com/sstephenson/bats/issues/49)
 * [Using `|| return 1` instead of `|| false`](https://github.com/bats-core/bats-core/commit/e5695a673faad4d4d33446ed5c99d70dbfa6d8be)
+
+
+### Set variable `__bp_inside_test` to test bash-preexec
+
+By default, bash-preexec is disabled in a non-interactive shell.  However, to
+test bash-preexec in non-interactive shells, one needs to enable bash-preexec
+by setting variable `__bp_inside_test` to a non-empty string.
+
+```bash
+__bp_inside_test=yes
+```
diff --git a/test/bash-preexec.bats b/test/bash-preexec.bats
index 152d5a6..c1593ea 100644
--- a/test/bash-preexec.bats
+++ b/test/bash-preexec.bats
@@ -1,5 +1,11 @@
 #!/usr/bin/env bats
 
+# This variable tells bash-preexec.sh that it is loaded for testing purposes.
+# bash-preexec.sh is intended to be used in interactive shell sessions, so it
+# is disabled in non-interactive shells by default.  However, it still needs to
+# be loaded in non-interactive shells for the Bats tests,
+__bp_inside_test=yes
+
 setup() {
   PROMPT_COMMAND=''        # in case the invoking shell has set this
   history -s fake command  # preexec requires there be some history
diff --git a/test/include-test.bats b/test/include-test.bats
index 36a5f25..7d2bc38 100644
--- a/test/include-test.bats
+++ b/test/include-test.bats
@@ -1,5 +1,11 @@
 #!/usr/bin/env bats
 
+# This variable tells bash-preexec.sh that it is loaded for testing purposes.
+# bash-preexec.sh is intended to be used in interactive shell sessions, so it
+# is disabled in non-interactive shells by default.  However, it still needs to
+# be loaded in non-interactive shells for the Bats tests,
+__bp_inside_test=yes
+
 @test "should not import if it's already defined" {
   bash_preexec_imported="defined"
   source "${BATS_TEST_DIRNAME}/../bash-preexec.sh"