diff --git a/pmd-core/src/main/java/net/sourceforge/pmd/util/ResourceLoader.java b/pmd-core/src/main/java/net/sourceforge/pmd/util/ResourceLoader.java
index ec7ccd1e47..61c5087b23 100644
--- a/pmd-core/src/main/java/net/sourceforge/pmd/util/ResourceLoader.java
+++ b/pmd-core/src/main/java/net/sourceforge/pmd/util/ResourceLoader.java
@@ -10,7 +10,9 @@ import java.io.FileNotFoundException;
 import java.io.IOException;
 import java.io.InputStream;
 import java.net.HttpURLConnection;
+import java.net.JarURLConnection;
 import java.net.URL;
+import java.net.URLConnection;
 
 import net.sourceforge.pmd.RuleSetNotFoundException;
 
@@ -41,6 +43,8 @@ public final class ResourceLoader {
      * Method to find a file, first by finding it as a file (either by the
      * absolute or relative path), then as a URL, and then finally seeing if it
      * is on the classpath.
+     * <p>
+     * Caller is responsible for closing the {@link InputStream}.
      *
      * @param name
      *            String
@@ -59,6 +63,8 @@ public final class ResourceLoader {
     /**
      * Uses the ClassLoader passed in to attempt to load the resource if it's
      * not a File or a URL
+     * <p>
+     * Caller is responsible for closing the {@link InputStream}.
      *
      * @param name
      *            String
@@ -91,8 +97,30 @@ public final class ResourceLoader {
                     if (resource == null) {
                         // Don't throw RuleSetNotFoundException, keep API compatibility
                         return null;
+                    } else {
+                        final URLConnection connection = resource.openConnection();
+                        final InputStream inputStream = connection.getInputStream();
+                        if (connection instanceof JarURLConnection) {
+                            // Wrap the InputStream to also close the underlying JarFile if from a JarURLConnection.
+                            // See https://github.com/pmd/pmd/issues/337
+                            return new InputStream() {
+                                @Override
+                                public int read() throws IOException {
+                                    return inputStream.read();
+                                }
+
+                                @Override
+                                public void close() throws IOException {
+                                    inputStream.close();
+                                    if (connection instanceof JarURLConnection) {
+                                        ((JarURLConnection) connection).getJarFile().close();
+                                    }
+                                }
+                            };
+                        } else {
+                            return inputStream;
+                        }
                     }
-                    return resource.openStream();
                 } catch (IOException e1) {
                     // Ignored
                 }
diff --git a/pmd-core/src/test/java/net/sourceforge/pmd/RuleSetFactoryTest.java b/pmd-core/src/test/java/net/sourceforge/pmd/RuleSetFactoryTest.java
index cb9f003dd0..252c346450 100644
--- a/pmd-core/src/test/java/net/sourceforge/pmd/RuleSetFactoryTest.java
+++ b/pmd-core/src/test/java/net/sourceforge/pmd/RuleSetFactoryTest.java
@@ -55,6 +55,7 @@ public class RuleSetFactoryTest {
         InputStream in = ResourceLoader.loadResourceAsStream("net/sourceforge/pmd/rulesets/reference-ruleset.xml",
                 this.getClass().getClassLoader());
         Assert.assertNotNull("Test ruleset not found - can't continue with test!", in);
+        in.close();
 
         RuleSetFactory rsf = new RuleSetFactory();
         RuleSets rs = rsf.createRuleSets("net/sourceforge/pmd/rulesets/reference-ruleset.xml");
diff --git a/pmd-test/src/main/java/net/sourceforge/pmd/AbstractRuleSetFactoryTest.java b/pmd-test/src/main/java/net/sourceforge/pmd/AbstractRuleSetFactoryTest.java
index e6f4d81647..38c7c12b59 100644
--- a/pmd-test/src/main/java/net/sourceforge/pmd/AbstractRuleSetFactoryTest.java
+++ b/pmd-test/src/main/java/net/sourceforge/pmd/AbstractRuleSetFactoryTest.java
@@ -229,7 +229,9 @@ public abstract class AbstractRuleSetFactoryTest {
         List<String> ruleSetFileNames = new ArrayList<>();
         try {
             Properties properties = new Properties();
-            properties.load(ResourceLoader.loadResourceAsStream("rulesets/" + language + "/rulesets.properties"));
+            try (InputStream is = ResourceLoader.loadResourceAsStream("rulesets/" + language + "/rulesets.properties")) {
+                properties.load(is);
+            }
             String fileNames = properties.getProperty("rulesets.filenames");
             StringTokenizer st = new StringTokenizer(fileNames, ",");
             while (st.hasMoreTokens()) {