diff --git a/solr/CHANGES.txt b/solr/CHANGES.txt
index 733fcd5b863..0d21c670b2a 100644
--- a/solr/CHANGES.txt
+++ b/solr/CHANGES.txt
@@ -242,6 +242,8 @@ Bug Fixes
 
 * SOLR-7666: Many small fixes to Angular UI (Upayavira, Alexandre Rafalovitch)
 
+* SOLR-7967: AddSchemaFieldsUpdateProcessorFactory does not check if the ConfigSet is immutable (Gregory Chanan)
+
 Optimizations
 ----------------------
 
diff --git a/solr/core/src/java/org/apache/solr/update/processor/AddSchemaFieldsUpdateProcessorFactory.java b/solr/core/src/java/org/apache/solr/update/processor/AddSchemaFieldsUpdateProcessorFactory.java
index e7ce92887e5..d388e7e91e6 100644
--- a/solr/core/src/java/org/apache/solr/update/processor/AddSchemaFieldsUpdateProcessorFactory.java
+++ b/solr/core/src/java/org/apache/solr/update/processor/AddSchemaFieldsUpdateProcessorFactory.java
@@ -47,6 +47,7 @@ import java.util.Set;
 
 import static org.apache.solr.common.SolrException.ErrorCode.BAD_REQUEST;
 import static org.apache.solr.common.SolrException.ErrorCode.SERVER_ERROR;
+import static org.apache.solr.core.ConfigSetProperties.IMMUTABLE_CONFIGSET_ARG;
 
 
 /**
@@ -290,6 +291,9 @@ public class AddSchemaFieldsUpdateProcessorFactory extends UpdateRequestProcesso
           // nothing to do - no fields will be added - exit from the retry loop
           log.debug("No fields to add to the schema.");
           break;
+        } else if ( isImmutableConfigSet(core) ) {
+          final String message = "This ConfigSet is immutable.";
+          throw new SolrException(BAD_REQUEST, message);
         }
         if (log.isDebugEnabled()) {
           StringBuilder builder = new StringBuilder();
@@ -399,5 +403,11 @@ public class AddSchemaFieldsUpdateProcessorFactory extends UpdateRequestProcesso
       }
       return selector;
     }
+
+    private boolean isImmutableConfigSet(SolrCore core) {
+      NamedList args = core.getConfigSetProperties();
+      Object immutable = args != null ? args.get(IMMUTABLE_CONFIGSET_ARG) : null;
+      return immutable != null ? Boolean.parseBoolean(immutable.toString()) : false;
+    }
   }
 }
diff --git a/solr/core/src/test/org/apache/solr/core/TestConfigSetImmutable.java b/solr/core/src/test/org/apache/solr/core/TestConfigSetImmutable.java
index 02e48770dd7..6347ae1eafd 100644
--- a/solr/core/src/test/org/apache/solr/core/TestConfigSetImmutable.java
+++ b/solr/core/src/test/org/apache/solr/core/TestConfigSetImmutable.java
@@ -23,6 +23,8 @@ import java.util.Map;
 
 import org.apache.commons.io.FileUtils;
 import org.apache.solr.SolrTestCaseJ4;
+import org.apache.solr.client.solrj.impl.XMLResponseParser;
+import org.apache.solr.common.util.NamedList;
 import org.apache.solr.util.RestTestBase;
 import org.junit.After;
 import org.junit.Before;
@@ -48,9 +50,8 @@ public class TestConfigSetImmutable extends RestTestBase {
     FileUtils.write(new File(tmpConfDir, "configsetprops.json"), new StringBuilder("{\"immutable\":\"true\"}"));
 
     System.setProperty("managed.schema.mutable", "true");
-    System.setProperty("enable.update.log", "false");
 
-    createJettyAndHarness(tmpSolrHome.getAbsolutePath(), "solrconfig-managed-schema.xml", "schema-rest.xml",
+    createJettyAndHarness(tmpSolrHome.getAbsolutePath(), "solrconfig-schemaless.xml", "schema-rest.xml",
         "/solr", true, null);
   }
 
@@ -95,4 +96,24 @@ public class TestConfigSetImmutable extends RestTestBase {
     assertNotNull(map.get("errors"));
     assertTrue(map.get("errors").toString().contains("immutable"));
   }
+
+  @Test
+  public void testAddSchemaFieldsImmutable() throws Exception {
+    final String error = "error";
+
+    // check writing an existing field is okay
+    String updateXMLSafe = "<add><doc><field name=\"id\">\"testdoc\"</field></doc></add>";
+    String response = restTestHarness.update(updateXMLSafe);
+    XMLResponseParser parser = new XMLResponseParser();
+    NamedList<Object> listResponse = parser.processResponse(new StringReader(response));
+    assertNull(listResponse.get(error));
+
+    // check writing a new field is not okay
+    String updateXMLNotSafe = "<add><doc><field name=\"id\">\"testdoc\"</field>" +
+        "<field name=\"newField67\">\"foobar\"</field></doc></add>";
+    response = restTestHarness.update(updateXMLNotSafe);
+    listResponse = parser.processResponse(new StringReader(response));
+    assertNotNull(listResponse.get(error));
+    assertTrue(listResponse.get(error).toString().contains("immutable"));
+  }
 }