diff --git a/README.md b/README.md
index e686fb7..67589ef 100644
--- a/README.md
+++ b/README.md
@@ -1,4 +1,4 @@
-# Fast builds for repositories using php-actions.
+# Fast builds for repositories using php-actions
 
 v1 of this repository used a totally different architecture and had different goals to the current version. Previously, a customised Dockerfile was used as the base for all php-actions repositories, but now php-actions workflows run as [composite run steps][composite], building a customised docker image per-application, based off the official PHP script.
 
@@ -25,7 +25,7 @@ Choosing the PHP version
 
 The `ACTION_PHP_VERSION` environment variable must be passed to the composite run step. This string must match any of the [officially supported PHP version numbers][tag-list] (version number only, with no derivative text, e.g. `8.0.1` or `8` rather than `8-cli`).
 
-The official Alpine CLI build of the requested version will be used as the image's base. 
+The official Alpine CLI build of the requested version will be used as the image's base.
 
 Enabling/disabling extensions
 -----------------------------
@@ -46,7 +46,7 @@ Version caching php-build
 
 This repo, `php-build` shouldn't change very regularly, but when it does, the entire build pipeline of dependent repositories will need refreshing. This is done by adding the version of `php-build` to the end of build package names. When a new release is made that affects php-build functionality, the variable at the top of `php-build.bash` can be updated to invalidate any caches.
 
-Within other repositories that use `php-build`, they can refer to the specific version of the script by addressing its git commit hash. For example: https://raw.githubusercontent.com/php-actions/php-build/27be075494ae8a9bc0d10deb408e37b197986b8a/php-build.bash
+Within other repositories that use `php-build`, they can refer to the specific version of the script by addressing its git commit hash. For example: <https://raw.githubusercontent.com/php-actions/php-build/27be075494ae8a9bc0d10deb408e37b197986b8a/php-build.bash>
 
 ***
 
@@ -57,5 +57,4 @@ If you found this repository helpful, please consider [sponsoring the developer]
 [tag-list]: https://github.com/docker-library/docs/blob/master/php/README.md#supported-tags-and-respective-dockerfile-links
 [mlocati]: https://github.com/mlocati/docker-php-extension-installer
 [mlocati-readme]: https://github.com/mlocati/docker-php-extension-installer#supported-php-extensions
-[issues]: https://github.com/php-actions/php-build/issues
 [sponsor]: https://github.com/sponsors/g105b
diff --git a/php-build.bash b/php-build.bash
old mode 100644
new mode 100755
index b977aca..165d252
--- a/php-build.bash
+++ b/php-build.bash
@@ -1,7 +1,7 @@
 #!/bin/bash
 set -e
 
-php_build_version="build2.1.1"
+php_build_version="build2.2.1"
 
 # Check for required variables:
 if [ "$#" -lt 1 ]; then
@@ -88,8 +88,8 @@ dockerfile_unique="${dockerfile_unique,,}"
 repo_without_org=$(echo "$GITHUB_REPOSITORY" | sed "s/[^\/]*\///")
 
 # This tag will be used to identify the built dockerfile. Once it is built,
-# it should not need to be built again, so after the first Github Actions run
-# the build should be very quick.
+# it should not need to be built again unless there is a PHP update, so after
+# the first Github Actions run the build should be very quick.
 # Note: The GITHUB_REPOSITORY is the repo where the action is running, nothing
 # to do with the php-actions organisation. This means that the image is pushed
 # onto a user's Github profile (currently not shared between other users).
@@ -104,7 +104,23 @@ echo "Pulling $docker_tag" >> output.log 2>&1
 # No need to continue building the image if the pull was successful.
 if docker pull "$docker_tag" >> output.log 2>&1;
 then
-	exit
+	# Unless the PHP version has an update...
+
+	# Pull latest PHP Docker image so we can check its version.
+	echo "Pulling $base_image" >> output.log 2>&1
+	docker pull "$base_image" >> output.log 2>&1
+
+	# Check PHP versions of the latest PHP tag and our tag.
+	base_image_php_version=$(docker run -i "$base_image" php -r "echo PHP_VERSION;")
+	cached_image_php_version=$(docker run -i "$docker_tag" php -r "echo PHP_VERSION;")
+
+	echo "Comparing $cached_image_php_version (cached) to $base_image_php_version (latest)." >> output.log 2>&1
+
+	# No need to continue building if our image already exists and PHP is up-to-date.
+	if [ $cached_image_php_version == $base_image_php_version ];
+	then
+		exit
+	fi
 fi
 
 echo "Building PHP $ACTION_PHP_VERSION with extensions: $ACTION_PHP_EXTENSIONS ..."