diff --git a/source/java/org/alfresco/repo/webdav/LockMethod.java b/source/java/org/alfresco/repo/webdav/LockMethod.java
index acc8560da4..42e54bff6c 100644
--- a/source/java/org/alfresco/repo/webdav/LockMethod.java
+++ b/source/java/org/alfresco/repo/webdav/LockMethod.java
@@ -368,6 +368,15 @@ public class LockMethod extends WebDAVMethod
         if (hasLockToken())
         {
             lockInfo = checkNode(lockNodeInfo);
+
+            if (!lockInfo.isLocked() && m_request.getContentLength() == -1)
+            {
+                // MNT-11990 fix, LOCK method with If header and without body was sent, according to RFC 2518 section 7.8
+                // this form of LOCK MUST only be used to "refresh" a lock. But node is not actually locked. Fail this request.
+                // see http://www.ics.uci.edu/~ejw/authoring/protocol/rfc2518.html#rfc.section.7.8
+                throw new WebDAVServerException(HttpServletResponse.SC_BAD_REQUEST);
+            }
+            
             // If a request body is not defined and "If" header is sent we have createExclusive as false,
             // but we need to check a previous LOCK was an exclusive. I.e. get the property for node. It
             // is already has got in a checkNode method, so we need just get a scope from lockInfo.
diff --git a/source/test-java/org/alfresco/repo/webdav/LockMethodTest.java b/source/test-java/org/alfresco/repo/webdav/LockMethodTest.java
index 427360cd0c..2f3142b93f 100644
--- a/source/test-java/org/alfresco/repo/webdav/LockMethodTest.java
+++ b/source/test-java/org/alfresco/repo/webdav/LockMethodTest.java
@@ -22,6 +22,7 @@ import static org.junit.Assert.assertEquals;
 import static org.junit.Assert.assertFalse;
 import static org.junit.Assert.assertNotNull;
 import static org.junit.Assert.assertTrue;
+import static org.junit.Assert.fail;
 
 import java.io.Serializable;
 import java.util.Collections;
@@ -338,4 +339,38 @@ public class LockMethodTest
         assertFalse("File should note exist in repo any more.", nodeService.exists(nodeRef));
         assertFalse("File should note exist in trashcan.", nodeService.exists(new NodeRef(StoreRef.STORE_REF_ARCHIVE_SPACESSTORE, nodeRef.getId())));
     }
+    
+    @Test
+    public void testMNT_11990() throws Exception
+    {
+        MockHttpServletRequest lockRequest = new MockHttpServletRequest(); 
+        lockRequest.addHeader(WebDAV.HEADER_TIMEOUT, WebDAV.SECOND + 3600);        
+        lockRequest.addHeader(WebDAV.HEADER_IF, "(<" + WebDAV.makeLockToken(fileNodeRef, userName) + ">)");
+        lockRequest.setRequestURI("/" + TEST_FILE_NAME);
+
+        lockMethod.setDetails(lockRequest, new MockHttpServletResponse(), davHelper, folderNodeRef);
+        lockMethod.parseRequestHeaders();
+        lockMethod.parseRequestBody();
+        
+        RetryingTransactionCallback<Void> lockExecuteImplCallBack = new RetryingTransactionCallback<Void>()
+        {
+            @Override
+            public Void execute() throws Throwable
+            {
+                try
+                {
+                    lockMethod.executeImpl();
+                    fail("Lock should not be refreshed for non-locked file.");
+                }
+                catch (WebDAVServerException e)
+                {
+                    assertEquals(e.getHttpStatusCode(), HttpServletResponse.SC_BAD_REQUEST);
+                }
+                return null;
+            }
+        };
+        
+        // try to refresh lock for non-locked node        
+        this.transactionService.getRetryingTransactionHelper().doInTransaction(lockExecuteImplCallBack);
+    }
 }