diff --git a/server/src/main/java/com/mirth/connect/plugins/datatypes/hl7v2/HL7v2ResponseValidator.java b/server/src/main/java/com/mirth/connect/plugins/datatypes/hl7v2/HL7v2ResponseValidator.java
index 165366b5d3..1e56533ed3 100644
--- a/server/src/main/java/com/mirth/connect/plugins/datatypes/hl7v2/HL7v2ResponseValidator.java
+++ b/server/src/main/java/com/mirth/connect/plugins/datatypes/hl7v2/HL7v2ResponseValidator.java
@@ -82,6 +82,8 @@ public Response validate(Response response, ConnectorMessage connectorMessage) {
                         } else {
                             response.setStatus(Status.SENT);
                         }
+                    } else {
+                        handleInvalidACK(response);
                     }
                 } else {
                     // ER7 response received
@@ -175,9 +177,7 @@ public Response validate(Response response, ConnectorMessage connectorMessage) {
                     }
 
                     if (!valid) {
-                        response.setStatus(Status.QUEUED);
-                        response.setStatusMessage("Invalid HL7 v2.x acknowledgement received.");
-                        response.setError(response.getStatusMessage());
+                        handleInvalidACK(response);
                     }
                 }
             } catch (Exception e) {
@@ -300,6 +300,12 @@ private void handleNACK(Response response, boolean rejected, String msa3, String
         response.setError(nackMessage.toString());
     }
 
+    private void handleInvalidACK(Response response) {
+        response.setStatus(Status.QUEUED);
+        response.setStatusMessage("Invalid HL7 v2.x acknowledgement received.");
+        response.setError(response.getStatusMessage());
+    }
+
     private void handleInvalidControlId(Response response, String originalControlID, String msa2) {
         response.setStatus(Status.ERROR);
 
diff --git a/server/src/test/java/com/mirth/connect/plugins/datatypes/hl7v2/HL7v2ResponseValidatorTest.java b/server/src/test/java/com/mirth/connect/plugins/datatypes/hl7v2/HL7v2ResponseValidatorTest.java
index abdacf9740..ef576bd427 100644
--- a/server/src/test/java/com/mirth/connect/plugins/datatypes/hl7v2/HL7v2ResponseValidatorTest.java
+++ b/server/src/test/java/com/mirth/connect/plugins/datatypes/hl7v2/HL7v2ResponseValidatorTest.java
@@ -236,13 +236,20 @@ public void testXmlErrorAndRejectedAcks() {
         assertEquals("NACK sent from receiver. (Rejected)", validate("<HL7Message><MSA><MSA.1>CR</MSA.1></MSA></HL7Message>").getStatusMessage());
     }
 
-    /*
-     * Characterizes existing behaviour: an unknown ACK code in an ER7 response is QUEUED as invalid
-     * (see testUnknownAckCodeIsInvalid), but in an XML response the status is left as it was.
-     */
     @Test
-    public void testXmlUnknownAckCodeLeavesStatusUnchanged() {
-        assertEquals(Status.SENT, validate("<HL7Message><MSA><MSA.1>XX</MSA.1></MSA></HL7Message>").getStatus());
+    public void testXmlUnknownAckCodeIsInvalid() {
+        Response response = validate("<HL7Message><MSA><MSA.1>XX</MSA.1></MSA></HL7Message>");
+
+        assertEquals(Status.QUEUED, response.getStatus());
+        assertEquals("Invalid HL7 v2.x acknowledgement received.", response.getStatusMessage());
+    }
+
+    @Test
+    public void testXmlMissingMsaIsInvalid() {
+        Response response = validate("<HL7Message><MSH><MSH.9><MSH.9.1>ACK</MSH.9.1></MSH.9></MSH></HL7Message>");
+
+        assertEquals(Status.QUEUED, response.getStatus());
+        assertEquals("Invalid HL7 v2.x acknowledgement received.", response.getStatusMessage());
     }
 
     @Test