diff --git a/builder/pom.xml b/builder/pom.xml
index 24c374f..18f07d5 100644
--- a/builder/pom.xml
+++ b/builder/pom.xml
@@ -31,6 +31,7 @@
         <map-builder.version>1.0.0</map-builder.version>
         <mockito.version>2.13.0</mockito.version>
         <assertj.version>3.9.0</assertj.version>
+        <fast-classpath-scanner.version>2.18.1</fast-classpath-scanner.version>
 
         <maven-checkstyle-plugin.version>3.0.0</maven-checkstyle-plugin.version>
         <kemitix.checkstyle.ruleset.version>${project.version}</kemitix.checkstyle.ruleset.version>
@@ -58,6 +59,11 @@
             <version>${lombok.version}</version>
             <scope>provided</scope>
         </dependency>
+        <dependency>
+            <groupId>io.github.lukehutch</groupId>
+            <artifactId>fast-classpath-scanner</artifactId>
+            <version>${fast-classpath-scanner.version}</version>
+        </dependency>
         <dependency>
             <groupId>org.mockito</groupId>
             <artifactId>mockito-core</artifactId>
diff --git a/builder/src/main/java/net/kemitix/checkstyle/ruleset/builder/BuilderConfiguration.java b/builder/src/main/java/net/kemitix/checkstyle/ruleset/builder/BuilderConfiguration.java
index 626c729..d5c7a95 100644
--- a/builder/src/main/java/net/kemitix/checkstyle/ruleset/builder/BuilderConfiguration.java
+++ b/builder/src/main/java/net/kemitix/checkstyle/ruleset/builder/BuilderConfiguration.java
@@ -21,15 +21,12 @@
 
 package net.kemitix.checkstyle.ruleset.builder;
 
-import com.google.common.reflect.ClassPath;
 import org.springframework.context.annotation.Bean;
 import org.springframework.context.annotation.Configuration;
 
-import java.io.IOException;
 import java.util.AbstractMap;
 import java.util.List;
 import java.util.Map;
-import java.util.function.Function;
 import java.util.stream.Collectors;
 import java.util.stream.Stream;
 
@@ -41,18 +38,6 @@ import java.util.stream.Stream;
 @Configuration
 public class BuilderConfiguration {
 
-    /**
-     * Create the ClassPath used to scan packages.
-     *
-     * @return the ClassPath
-     *
-     * @throws IOException if there is an error
-     */
-    @Bean
-    public ClassPath classPath() throws IOException {
-        return ClassPath.from(getClass().getClassLoader());
-    }
-
     /**
      * A Map of rules for each RuleSource.
      *
@@ -63,24 +48,11 @@ public class BuilderConfiguration {
     @Bean
     public Map<RuleSource, List<String>> checkClasses(final PackageScanner packageScanner) {
         return Stream.of(RuleSource.values())
-                .map(toRuleSourceEntry(packageScanner))
+                .map(source -> entry(source, packageScanner.apply(source)))
                 .collect(Collectors.toMap(Map.Entry::getKey, Map.Entry::getValue));
     }
 
-    private static Function<RuleSource, AbstractMap.SimpleEntry<RuleSource, List<String>>> toRuleSourceEntry(
-            final PackageScanner packageScanner
-                                                                                                            ) {
-        return source -> new AbstractMap.SimpleEntry<>(
-                source,
-                classesInSource(source, packageScanner)
-        );
-    }
-
-    private static List<String> classesInSource(
-            final RuleSource source,
-            final PackageScanner packageScanner
-                                               ) {
-        return packageScanner.apply(source)
-                .collect(Collectors.toList());
+    private static <K, V> AbstractMap.SimpleEntry<K, V> entry(final K key, final V value) {
+        return new AbstractMap.SimpleEntry<>(key, value);
     }
 }
diff --git a/builder/src/main/java/net/kemitix/checkstyle/ruleset/builder/DefaultPackageScanner.java b/builder/src/main/java/net/kemitix/checkstyle/ruleset/builder/DefaultPackageScanner.java
index aea4769..f193f1b 100644
--- a/builder/src/main/java/net/kemitix/checkstyle/ruleset/builder/DefaultPackageScanner.java
+++ b/builder/src/main/java/net/kemitix/checkstyle/ruleset/builder/DefaultPackageScanner.java
@@ -21,11 +21,11 @@
 
 package net.kemitix.checkstyle.ruleset.builder;
 
-import com.google.common.reflect.ClassPath;
-import lombok.RequiredArgsConstructor;
+import io.github.lukehutch.fastclasspathscanner.FastClasspathScanner;
 import org.springframework.stereotype.Service;
 
-import java.util.stream.Stream;
+import java.util.List;
+import java.util.stream.Collectors;
 
 /**
  * Default implementation of {@link PackageScanner}.
@@ -33,15 +33,16 @@ import java.util.stream.Stream;
  * @author Paul Campbell (pcampbell@kemitix.net).
  */
 @Service
-@RequiredArgsConstructor
 public class DefaultPackageScanner implements PackageScanner {
 
-    private final ClassPath classPath;
-
     @Override
-    public final Stream<String> apply(final RuleSource ruleSource) {
-        return classPath.getTopLevelClassesRecursive(ruleSource.getBasePackage())
-                        .stream()
-                        .map(ClassPath.ClassInfo::getName);
+    public final List<String> apply(final RuleSource ruleSource) {
+        final String basePackage = ruleSource.getBasePackage();
+        return new FastClasspathScanner(basePackage)
+                .scan()
+                .getNamesOfAllStandardClasses()
+                .stream()
+                .filter(packageName -> packageName.startsWith(basePackage))
+                .collect(Collectors.toList());
     }
 }
diff --git a/builder/src/main/java/net/kemitix/checkstyle/ruleset/builder/PackageScanner.java b/builder/src/main/java/net/kemitix/checkstyle/ruleset/builder/PackageScanner.java
index 7cc8c2b..02a59df 100644
--- a/builder/src/main/java/net/kemitix/checkstyle/ruleset/builder/PackageScanner.java
+++ b/builder/src/main/java/net/kemitix/checkstyle/ruleset/builder/PackageScanner.java
@@ -21,14 +21,14 @@
 
 package net.kemitix.checkstyle.ruleset.builder;
 
+import java.util.List;
 import java.util.function.Function;
-import java.util.stream.Stream;
 
 /**
  * Scans a package for all classes.
  *
  * @author Paul Campbell (pcampbell@kemitix.net).
  */
-interface PackageScanner extends Function<RuleSource, Stream<String>> {
+interface PackageScanner extends Function<RuleSource, List<String>> {
 
 }
diff --git a/builder/src/test/java/net/kemitix/checkstyle/ruleset/builder/BuilderConfigurationTest.java b/builder/src/test/java/net/kemitix/checkstyle/ruleset/builder/BuilderConfigurationTest.java
index 9279196..f9afaa8 100644
--- a/builder/src/test/java/net/kemitix/checkstyle/ruleset/builder/BuilderConfigurationTest.java
+++ b/builder/src/test/java/net/kemitix/checkstyle/ruleset/builder/BuilderConfigurationTest.java
@@ -9,6 +9,7 @@ import java.util.List;
 import java.util.Map;
 import java.util.stream.Stream;
 
+import static java.util.Collections.singletonList;
 import static org.assertj.core.api.Assertions.assertThat;
 import static org.mockito.BDDMockito.given;
 import static org.mockito.Mockito.mock;
@@ -20,28 +21,20 @@ import static org.mockito.Mockito.mock;
  */
 public class BuilderConfigurationTest {
 
-    @Test
-    public void canGetClassPath() throws IOException {
-        //when
-        final ClassPath classPath = new BuilderConfiguration().classPath();
-        //then
-        assertThat(classPath).isNotNull();
-    }
-
     @Test
     public void canGetCheckClasses() {
         //given
         final PackageScanner packageScanner = mock(PackageScanner.class);
         final String checkstyleClass = "checkstyle class";
-        given(packageScanner.apply(RuleSource.CHECKSTYLE)).willReturn(Stream.of(checkstyleClass));
+        given(packageScanner.apply(RuleSource.CHECKSTYLE)).willReturn(singletonList(checkstyleClass));
         final String sevntuClass = "sevntu class";
-        given(packageScanner.apply(RuleSource.SEVNTU)).willReturn(Stream.of(sevntuClass));
+        given(packageScanner.apply(RuleSource.SEVNTU)).willReturn(singletonList(sevntuClass));
         //when
         final Map<RuleSource, List<String>> checkClasses = new BuilderConfiguration().checkClasses(packageScanner);
         //then
         assertThat(checkClasses).containsOnlyKeys(RuleSource.values());
         assertThat(checkClasses)
-                .containsEntry(RuleSource.CHECKSTYLE, Collections.singletonList(checkstyleClass))
-                .containsEntry(RuleSource.SEVNTU, Collections.singletonList(sevntuClass));
+                .containsEntry(RuleSource.CHECKSTYLE, singletonList(checkstyleClass))
+                .containsEntry(RuleSource.SEVNTU, singletonList(sevntuClass));
     }
 }
diff --git a/builder/src/test/java/net/kemitix/checkstyle/ruleset/builder/DefaultPackageScannerTest.java b/builder/src/test/java/net/kemitix/checkstyle/ruleset/builder/DefaultPackageScannerTest.java
index 240d12c..7b5a02e 100644
--- a/builder/src/test/java/net/kemitix/checkstyle/ruleset/builder/DefaultPackageScannerTest.java
+++ b/builder/src/test/java/net/kemitix/checkstyle/ruleset/builder/DefaultPackageScannerTest.java
@@ -1,10 +1,8 @@
 package net.kemitix.checkstyle.ruleset.builder;
 
-import com.google.common.reflect.ClassPath;
-import org.junit.Before;
 import org.junit.Test;
 
-import java.io.IOException;
+import java.util.List;
 import java.util.stream.Stream;
 
 import static org.assertj.core.api.Assertions.assertThat;
@@ -16,27 +14,21 @@ import static org.assertj.core.api.Assertions.assertThat;
  */
 public class DefaultPackageScannerTest {
 
-    private PackageScanner scanner;
-
-    @Before
-    public void setUp() throws Exception {
-        final ClassPath classPath = ClassPath.from(getClass().getClassLoader());
-        scanner = new DefaultPackageScanner(classPath);
-    }
+    private PackageScanner scanner = new DefaultPackageScanner();
 
     @Test
-    public void canScanCheckstylePackage() throws IOException {
+    public void canScanCheckstylePackage() {
         //when
-        final Stream<String> result = scanner.apply(RuleSource.CHECKSTYLE);
+        final List<String> result = scanner.apply(RuleSource.CHECKSTYLE);
         //then
         assertThat(result).allMatch(cn -> cn.startsWith(RuleSource.CHECKSTYLE.getBasePackage()))
                           .contains("com.puppycrawl.tools.checkstyle.checks.sizes.FileLengthCheck");
     }
 
     @Test
-    public void canScanSevntuPackage() throws IOException {
+    public void canScanSevntuPackage() {
         //when
-        final Stream<String> result = scanner.apply(RuleSource.SEVNTU);
+        final List<String> result = scanner.apply(RuleSource.SEVNTU);
         //then
         assertThat(result).allMatch(cn -> cn.startsWith(RuleSource.SEVNTU.getBasePackage()))
                           .contains("com.github.sevntu.checkstyle.checks.design.NestedSwitchCheck");