diff --git a/action.yml b/action.yml
index ff30972..c91bc26 100644
--- a/action.yml
+++ b/action.yml
@@ -45,6 +45,11 @@ inputs:
       This field will always try to follow Checkstyle releases as close as possible and will use the latest available by default.
       If it is not a default preference for your project, please, pin the needed version using this property.
     default: ""
+  checkstyle_classpath:
+    description: |
+      Classpath for checkstyle. This is needed when your checkstyle configuration uses custom checks that are not included in the default checkstyle distribution.
+      You can specify either a single jar file or a directory with multiple jar files. In the latter case, all jar files in the directory will be added to the classpath.
+    default: ""
   properties_file:
     description: |
       Location of the properties file relative to the root directory. This file serves as a means to resolve repetitive or predefined values within the checkstyle configuration file.
diff --git a/entrypoint.sh b/entrypoint.sh
index 3f90c38..eff6ddf 100755
--- a/entrypoint.sh
+++ b/entrypoint.sh
@@ -17,6 +17,11 @@ if [ -n "${INPUT_PROPERTIES_FILE}" ]; then
   OPTIONAL_PROPERTIES_FILE="-p ${INPUT_PROPERTIES_FILE}"
 fi
 
+CHECKSTYLE_CLASSPATH="/opt/lib/checkstyle.jar"
+if [ -n "${INPUT_CHECKSTYLE_CLASSPATH}" ]; then
+  CHECKSTYLE_CLASSPATH="${CHECKSTYLE_CLASSPATH}:${INPUT_CHECKSTYLE_CLASSPATH}"
+fi
+
 # user wants to use custom Checkstyle version, try to install it
 if [ -n "${INPUT_CHECKSTYLE_VERSION}" ]; then
   echo '::group::📥 Installing user-defined Checkstyle version ... https://github.com/checkstyle/checkstyle'
@@ -38,7 +43,11 @@ echo '::group:: Running Checkstyle with reviewdog 🐶 ...'
 { echo "Run check with"; java -jar /opt/lib/checkstyle.jar --version; } | sed ':a;N;s/\n/ /;ba'
 
 # shellcheck disable=SC2086
-exec java -jar /opt/lib/checkstyle.jar "${INPUT_WORKDIR}" -c "${INPUT_CHECKSTYLE_CONFIG}" ${OPTIONAL_PROPERTIES_FILE} -f xml \
+exec \
+  java \
+    -cp ${CHECKSTYLE_CLASSPATH} \
+    com.puppycrawl.tools.checkstyle.Main "${INPUT_WORKDIR}" \
+    -c "${INPUT_CHECKSTYLE_CONFIG}" ${OPTIONAL_PROPERTIES_FILE} -f xml \
   | reviewdog -f=checkstyle \
       -name="checkstyle" \
       -reporter="${INPUT_REPORTER:-github-pr-check}" \