diff --git a/rulesets/java-sheepit.xml b/rulesets/java-sheepit.xml
index eaee651..b2b2ac6 100644
--- a/rulesets/java-sheepit.xml
+++ b/rulesets/java-sheepit.xml
@@ -32,6 +32,7 @@
 	<rule ref="category/java/codestyle.xml/UselessQualifiedThis" />
 	<rule ref="category/java/design.xml/SimplifiedTernary" />
 	<rule ref="category/java/design.xml/UselessOverridingMethod" />
+	<rule ref="category/java/design.xml/ClassWithOnlyPrivateConstructorsShouldBeFinal" />
 	<rule ref="category/java/errorprone.xml/AvoidBranchingStatementAsLastInLoop" />
 	<rule ref="category/java/errorprone.xml/AvoidDecimalLiteralsInBigDecimalConstructor" />
 	<rule ref="category/java/errorprone.xml/AvoidMultipleUnaryOperators" />
diff --git a/src/main/java/com/sheepit/client/Log.java b/src/main/java/com/sheepit/client/Log.java
index 04d16e0..585a5d0 100644
--- a/src/main/java/com/sheepit/client/Log.java
+++ b/src/main/java/com/sheepit/client/Log.java
@@ -32,7 +32,7 @@ import java.util.HashMap;
 import java.util.Map;
 import java.util.Optional;
 
-public class Log {
+public final class Log {
 	private final String LEVEL_DEBUG = "debug";
 	private final String LEVEL_INFO = "info";
 	private final String LEVEL_ERROR = "error";
diff --git a/src/main/java/com/sheepit/client/hardware/gpu/nvidia/CUresult.java b/src/main/java/com/sheepit/client/hardware/gpu/nvidia/CUresult.java
index 4f75a09..7175dc9 100644
--- a/src/main/java/com/sheepit/client/hardware/gpu/nvidia/CUresult.java
+++ b/src/main/java/com/sheepit/client/hardware/gpu/nvidia/CUresult.java
@@ -33,7 +33,7 @@ package com.sheepit.client.hardware.gpu.nvidia;
  * <br />
  * Most comments are taken from the CUDA reference manual.
  */
-public class CUresult {
+public final class CUresult {
 	/**
 	 * The API call returned with no errors. In the case of query calls, this
 	 * can also mean that the operation being queried is complete (see