diff --git a/README.md b/README.md
index 2e49344..27dfa14 100644
--- a/README.md
+++ b/README.md
@@ -44,7 +44,7 @@ Inputs
 
 The following configuration options are available:
 
-+ `version` The version of PHPUnit to use e.g. `9` or `9.5.0` (default: latest)
++ `version` The version of PHPUnit to use e.g. `latest`, `9` or `9.5.0` (default: `composer` - use the version specified in composer.json)
 + `php_version` The version of PHP to use e.g. `7.4` (default: latest)
 + `php_extensions` Space-separated list of extensions using [php-build][php-build] e.g. `xdebug mbstring` (default: N/A)
 + `vendored_phpunit_path` The path to a phar file already present on the runner (default: N/A)
@@ -95,7 +95,7 @@ PHP and PHPUnit versions
 
 It's possible to run any version of PHPUnit under any version of PHP, with any PHP extensions you require. This is configured with the following inputs:
 
-+ `version` - the version number of PHPUnit to run e.g. `9` or `9.5.0` (default: latest)
++ `version` - the version number of PHPUnit to run e.g. `latest`, `9` or `9.5.0` (default: `composer`). Using the default value, `composer` will install the version specified in `composer.json`
 + `php_version` - the version number of PHP to use e.g. `7.4` (default: latest)
 + `php_extensions` - a space-separated list of extensions to install using [php-build][php-build] e.g. `xdebug mbstring` (default: N/A)
 
diff --git a/action.yml b/action.yml
index 4f492fb..671afea 100644
--- a/action.yml
+++ b/action.yml
@@ -4,7 +4,7 @@ description: Run your PHPUnit tests in your Github Actions.
 inputs:
   version:
     description: What version of PHPUnit to use
-    default: latest
+    default: composer
     required: false
 
   php_version:
diff --git a/phpunit-action.bash b/phpunit-action.bash
index 26ce162..a626f35 100755
--- a/phpunit-action.bash
+++ b/phpunit-action.bash
@@ -5,9 +5,28 @@ docker_tag=$(cat ./docker_tag)
 
 echo "Docker tag: $docker_tag" >> output.log 2>&1
 
+function get_version_from_composer() {
+	version_string="*"
+
+	if [ -f composer.lock ]
+	then
+		version_string=$(jq -r 'first(.["packages-dev"][]?, .packages[]? | select(.name == "phpunit/phpunit") | .version)' composer.lock)
+	else
+		version_string=$(jq '.["require-dev"]["phpunit/phpunit"] // .["require"]["phpunit/phpunit"]' composer.json)
+		version_string=$(echo "$version_string" | sed -E 's/^[^0-9]*//')
+	fi
+
+	echo $version_string
+}
+
 if [ -z "$ACTION_PHPUNIT_PATH" ]
 then
 	phar_url="https://phar.phpunit.de/phpunit"
+	if [ "$ACTION_VERSION" == "composer" ]
+	then
+		ACTION_VERSION=$(get_version_from_composer)
+	fi
+
 	if [ "$ACTION_VERSION" != "latest" ]
 	then
 		phar_url="${phar_url}-${ACTION_VERSION}"
@@ -135,6 +154,11 @@ fi
 
 echo "Command: ${command_string[@]}" >> output.log 2>&1
 
+me=$(whoami)
+echo "Current user: $me"
+
+ls -la
+
 docker run --rm \
 	--volume "${phar_path}":/usr/local/bin/phpunit \
 	--volume "${GITHUB_WORKSPACE}":/app \