diff --git a/plugin/src/main/java/org/jenkinsci/plugins/workflow/cps/CpsFlowExecution.java b/plugin/src/main/java/org/jenkinsci/plugins/workflow/cps/CpsFlowExecution.java
index 8550caf86..b79a42401 100644
--- a/plugin/src/main/java/org/jenkinsci/plugins/workflow/cps/CpsFlowExecution.java
+++ b/plugin/src/main/java/org/jenkinsci/plugins/workflow/cps/CpsFlowExecution.java
@@ -1306,8 +1306,18 @@ synchronized void onProgramEnd(Outcome outcome) {
 
     void cleanUpHeap() {
         LOGGER.log(Level.FINE, "cleanUpHeap on {0}", owner);
-        shell = null;
-        trusted = null;
+        try {
+            if (shell != null) {
+                shell.getClassLoader().close();
+                shell = null;
+            }
+            if (trusted != null) {
+                trusted.getClassLoader().close();
+                trusted = null;
+            }
+        } catch (IOException x) {
+            LOGGER.log(Level.WARNING, "failed to close class loaders from " + owner, x);
+        }
         if (scriptClass != null) {
             try {
                 cleanUpLoader(scriptClass.getClassLoader(), new HashSet<>(), new HashSet<>());