diff --git a/engine-core/src/main/java/io/nosqlbench/engine/core/script/ScriptParams.java b/engine-core/src/main/java/io/nosqlbench/engine/core/script/ScriptParams.java
index 2830626a5..e435490cd 100644
--- a/engine-core/src/main/java/io/nosqlbench/engine/core/script/ScriptParams.java
+++ b/engine-core/src/main/java/io/nosqlbench/engine/core/script/ScriptParams.java
@@ -18,36 +18,56 @@
 package io.nosqlbench.engine.core.script;
 
 import ch.qos.logback.classic.Logger;
+import com.google.gson.Gson;
+import com.google.gson.GsonBuilder;
 import io.nosqlbench.nb.api.errors.BasicError;
 import org.slf4j.LoggerFactory;
 
 import java.util.HashMap;
 import java.util.Map;
+import java.util.Set;
 import java.util.stream.Collectors;
 
+/**
+ * Wrap the script parameters in a type which allows for easy manipulation
+ */
 public class ScriptParams extends HashMap<String, String> {
 
     private static final Logger logger = (Logger) LoggerFactory.getLogger(ScriptParams.class);
+    private static final Gson gson = new GsonBuilder().setPrettyPrinting().create();
 
-    public Map<String, String> withOverrides(Map<String, String> overrides) {
+    public Map<String,String> withOverrides(Map<String, String> overrides) {
         if (overrides == null) {
             logger.warn("A null map was provided to withOverrides. This could be a bug in your script.");
             overrides=Map.of();
         }
         checkForNulls("params", "calling withOverrides", this);
         checkForNulls("overrides", "calling withOverrides", overrides);
-        HashMap<String, String> result = new HashMap<>();
+        ScriptParams result = new ScriptParams();
         result.putAll(this);
-        result.putAll(overrides);
+
+        for (Entry<String, String> overrideEntry : overrides.entrySet()) {
+            String oKey = overrideEntry.getKey();
+            String oVal = overrideEntry.getValue();
+            if (oVal.toUpperCase().endsWith("UNDEF")) {
+                String removed = result.remove(oKey);
+                logger.trace("Removed key '" + oKey + "': '" + removed + "' from script params because it was "+ oVal + " in overrides");
+            } else {
+                String was = result.get(oKey);
+                was = (was==null ? "NULL" : was);
+                result.put(oKey,oVal);
+                logger.trace("Overrode key '" + oKey + "': from '" + was + " to " + oVal);
+            }
+        }
         return result;
     }
 
-    public Map<String, String> withDefaults(Map<String, String> defaults) {
+    public Map<String,String> withDefaults(Map<String, String> defaults) {
         if (defaults == null) {
             logger.warn("A null map was provided to withDefaults. This could be a bug in your script.");
             defaults=Map.of();
         }
-        HashMap<String, String> result = new HashMap<>();
+        ScriptParams result = new ScriptParams();
         checkForNulls("params", "calling withDefaults", this);
         checkForNulls("defaults", "calling withDefaults", defaults);
         result.putAll(defaults);
@@ -78,6 +98,11 @@ public class ScriptParams extends HashMap<String, String> {
         logger.info(mapdetail);
     }
 
+    @Override
+    public String toString() {
+        return gson.toJson(this,Map.class).toString();
+    }
+
     private static String valueOf(Object o) {
         if (o == null) {
             return "NULL";
diff --git a/nb/src/test/java/io/nosqlbench/engine/core/script/AsyncScriptIntegrationTests.java b/nb/src/test/java/io/nosqlbench/engine/core/script/AsyncScriptIntegrationTests.java
index 24c96a820..e7a46e521 100644
--- a/nb/src/test/java/io/nosqlbench/engine/core/script/AsyncScriptIntegrationTests.java
+++ b/nb/src/test/java/io/nosqlbench/engine/core/script/AsyncScriptIntegrationTests.java
@@ -161,6 +161,13 @@ public class AsyncScriptIntegrationTests {
         assertThat(scenarioResult.getIOLog()).contains("params.get(\"four\") [defaulted-four-niner]='niner'");
     }
 
+    @Test
+    public void testScriptParamsUndefVariableWithOverride() {
+        ScenarioResult scenarioResult = runScenario("undef_param", "one", "two", "three", "four");
+        assertThat(scenarioResult.getIOLog()).contains("before: params.get(\"three\"):four");
+        assertThat(scenarioResult.getIOLog()).contains("after: params.get(\"three\"):null");
+    }
+
     @Test
     public void testExtensionHistoStatsLogger() throws IOException {
         ScenarioResult scenarioResult = runScenario("extension_histostatslogger");
diff --git a/nb/src/test/resources/scripts/async/undef_param.js b/nb/src/test/resources/scripts/async/undef_param.js
new file mode 100644
index 000000000..5ba310d1e
--- /dev/null
+++ b/nb/src/test/resources/scripts/async/undef_param.js
@@ -0,0 +1,16 @@
+print("params from command line:");
+print(params);
+print('before: params.get("three"):' + params.get("three"));
+print('before: params.three:' + params.get("three"));
+
+var overrides = {
+  'three': "undef",
+};
+
+print("params.three after overriding with three:UNDEF");
+params = params.withOverrides({'three':'UNDEF'});
+print(params);
+print('after: params.get("three"):' + params.get("three"));
+print('after: params.three:' + params.get("three"));
+
+