diff --git a/.github/workflows/tests.yml b/.github/workflows/tests.yml
index 9b748c9..42f7e74 100644
--- a/.github/workflows/tests.yml
+++ b/.github/workflows/tests.yml
@@ -28,7 +28,7 @@ jobs:
         uses: actions/setup-java@v4
         with:
           distribution: 'corretto'
-          java-version: '21'
+          java-version: '23'
 
       - name: Test with Maven
         run: mvn test
diff --git a/pom.xml b/pom.xml
index 4dbc741..9f28b3b 100644
--- a/pom.xml
+++ b/pom.xml
@@ -8,15 +8,15 @@
 	<version>1.0.9</version>
 	<name>C S 240 Checkstyle Checks</name>
 	<properties>
-		<maven.compiler.source>21</maven.compiler.source>
-		<maven.compiler.target>21</maven.compiler.target>
+		<maven.compiler.source>23</maven.compiler.source>
+		<maven.compiler.target>23</maven.compiler.target>
 		<project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
 	</properties>
 	<dependencies>
 		<dependency>
 			<groupId>com.puppycrawl.tools</groupId>
 			<artifactId>checkstyle</artifactId>
-			<version>10.14.1</version>
+			<version>13.5.0</version>
 		</dependency>
 		<dependency>
 			<groupId>org.junit.jupiter</groupId>
diff --git a/src/main/resources/cs240_checks.xml b/src/main/resources/cs240_checks.xml
index 4b1df99..e62b879 100644
--- a/src/main/resources/cs240_checks.xml
+++ b/src/main/resources/cs240_checks.xml
@@ -41,17 +41,17 @@
                      value="Parameter name ''{0}'' must match pattern ''{1}'' (lowerCamelCase)."/>
         </module>
         <module name="LambdaParameterName">
-            <property name="format" value="^[a-z][a-zA-Z0-9]*$"/>
+            <property name="format" value="^[a-z][a-zA-Z0-9]*|_$"/>
             <message key="name.invalidPattern"
                      value="Lambda parameter name ''{0}'' must match pattern ''{1}'' (lowerCamelCase)."/>
         </module>
         <module name="CatchParameterName">
-            <property name="format" value="^[a-z][a-zA-Z0-9]*$"/>
+            <property name="format" value="^[a-z][a-zA-Z0-9]*|_$"/>
             <message key="name.invalidPattern"
                      value="Catch parameter name ''{0}'' must match pattern ''{1}'' (lowerCamelCase)."/>
         </module>
         <module name="LocalVariableName">
-            <property name="format" value="^[a-z][a-zA-Z0-9]*$"/>
+            <property name="format" value="^[a-z][a-zA-Z0-9]*|_$"/>
             <message key="name.invalidPattern"
                      value="Local variable name ''{0}'' must match pattern ''{1}'' (lowerCamelCase)."/>
         </module>
@@ -61,7 +61,7 @@
                      value="Local variable name ''{0}'' must match pattern ''{1}'' (lowerCamelCase)."/>
         </module>
         <module name="PatternVariableName">
-            <property name="format" value="^[a-z][a-zA-Z0-9]*$"/>
+            <property name="format" value="^[a-z][a-zA-Z0-9]*|_$"/>
             <message key="name.invalidPattern"
                      value="Pattern variable name ''{0}'' must match pattern ''{1}'' (lowerCamelCase)."/>
         </module>