diff --git a/modules/openapi-generator-core/src/main/java/org/openapitools/codegen/config/WorkflowSettings.java b/modules/openapi-generator-core/src/main/java/org/openapitools/codegen/config/WorkflowSettings.java
index bf13cacf7b2..174109f37b9 100644
--- a/modules/openapi-generator-core/src/main/java/org/openapitools/codegen/config/WorkflowSettings.java
+++ b/modules/openapi-generator-core/src/main/java/org/openapitools/codegen/config/WorkflowSettings.java
@@ -103,7 +103,9 @@ public class WorkflowSettings {
         builder.strictSpecBehavior = copy.isStrictSpecBehavior();
         builder.templatingEngineName = copy.getTemplatingEngineName();
         builder.ignoreFileOverride = copy.getIgnoreFileOverride();
-        builder.systemProperties = ImmutableMap.copyOf(copy.getSystemProperties());
+
+        // this, and any other collections, must be mutable in the builder.
+        builder.systemProperties = new HashMap<>(copy.getSystemProperties());
 
         // force builder "with" methods to invoke side effects
         builder.withTemplateDir(copy.getTemplateDir());
@@ -272,6 +274,8 @@ public class WorkflowSettings {
         private String templateDir;
         private String templatingEngineName = DEFAULT_TEMPLATING_ENGINE_NAME;
         private String ignoreFileOverride;
+
+        // NOTE: All collections must be mutable in the builder, and copied to a new immutable collection in .build()
         private Map<String, String> systemProperties = new HashMap<>();;
 
         private Builder() {
diff --git a/modules/openapi-generator-core/src/test/java/org/openapitools/codegen/config/WorkflowSettingsTest.java b/modules/openapi-generator-core/src/test/java/org/openapitools/codegen/config/WorkflowSettingsTest.java
index b958c9decf4..c375e98df2c 100644
--- a/modules/openapi-generator-core/src/test/java/org/openapitools/codegen/config/WorkflowSettingsTest.java
+++ b/modules/openapi-generator-core/src/test/java/org/openapitools/codegen/config/WorkflowSettingsTest.java
@@ -19,6 +19,7 @@ package org.openapitools.codegen.config;
 import org.testng.annotations.Test;
 
 import java.nio.file.Paths;
+import java.util.Map;
 
 import static org.testng.Assert.*;
 
@@ -48,6 +49,25 @@ public class WorkflowSettingsTest {
         assertTrue(settings.isStrictSpecBehavior());
     }
 
+    @Test
+    public void newBuilderFromCopyShouldMutateSystemProperties(){
+        WorkflowSettings original = WorkflowSettings.newBuilder()
+                .withOutputDir("output")
+                .withVerbose(true)
+                .withSkipOverwrite(false)
+                .withSystemProperty("first", "1st")
+                .build();
+
+        WorkflowSettings modified = WorkflowSettings.newBuilder(original)
+                .withSystemProperty("second", "2nd")
+                .build();
+
+        Map<String, String> properties = modified.getSystemProperties();
+        assertEquals(properties.size(), 2, "System Properties map should allow mutation when invoked via copy constructor");
+        assertEquals(properties.getOrDefault("first", ""), "1st");
+        assertEquals(properties.getOrDefault("second", ""), "2nd");
+    }
+
     private void assertOnChangesToDefaults(WorkflowSettings defaults) {
         WorkflowSettings settings = WorkflowSettings.newBuilder()
                 .withOutputDir("output")
diff --git a/modules/openapi-generator-gradle-plugin/samples/local-spec/README.md b/modules/openapi-generator-gradle-plugin/samples/local-spec/README.md
index 702381eed21..7d4ba57448f 100644
--- a/modules/openapi-generator-gradle-plugin/samples/local-spec/README.md
+++ b/modules/openapi-generator-gradle-plugin/samples/local-spec/README.md
@@ -11,6 +11,7 @@ gradle openApiGenerate
 gradle openApiMeta
 gradle openApiValidate
 gradle buildGoSdk
+gradle buildDotnetSdk
 gradle generateGoWithInvalidSpec
 ```
 
diff --git a/modules/openapi-generator-gradle-plugin/samples/local-spec/build.gradle b/modules/openapi-generator-gradle-plugin/samples/local-spec/build.gradle
index 68913ab6c2c..99e3d0f674c 100644
--- a/modules/openapi-generator-gradle-plugin/samples/local-spec/build.gradle
+++ b/modules/openapi-generator-gradle-plugin/samples/local-spec/build.gradle
@@ -65,6 +65,20 @@ task buildGoSdk(type: org.openapitools.generator.gradle.plugin.tasks.GenerateTas
     ]
 }
 
+task buildDotnetSdk(type: org.openapitools.generator.gradle.plugin.tasks.GenerateTask){
+    generatorName = "csharp-netcore"
+    inputSpec = "$rootDir/petstore-v3.0.yaml".toString()
+    additionalProperties = [
+            packageGuid: "{321C8C3F-0156-40C1-AE42-D59761FB9B6C}",
+            useCompareNetObjects: "true"
+    ]
+    outputDir = "$buildDir/csharp-netcore".toString()
+    systemProperties = [
+            models: "",
+            apis  : "",
+    ]
+}
+
 task generateGoWithInvalidSpec(type: org.openapitools.generator.gradle.plugin.tasks.GenerateTask){
     validateSpec = true
     generatorName = "go"