diff --git a/java/org/apache/coyote/ajp/AjpProcessor.java b/java/org/apache/coyote/ajp/AjpProcessor.java
index 93d671cb7fc8..ccf2e78ba1d5 100644
--- a/java/org/apache/coyote/ajp/AjpProcessor.java
+++ b/java/org/apache/coyote/ajp/AjpProcessor.java
@@ -956,43 +956,47 @@ protected final void prepareResponse() throws IOException {
         responseMsgPos = -1;
 
         int numHeaders = headers.size();
-        for (int i = 0; i < numHeaders; i++) {
-            if (i == 0) {
-                // Write AJP message header
-                responseMessage.reset();
-                responseMessage.appendByte(Constants.JK_AJP13_SEND_HEADERS);
-
-                // Write HTTP response line
-                responseMessage.appendInt(statusCode);
-                // Reason phrase is optional but mod_jk + httpd 2.x fails with a null
-                // reason phrase - bug 45026
-                tmpMB.setString(Integer.toString(response.getStatus()));
-                responseMessage.appendBytes(tmpMB);
-
-                // Start headers
-                responseMessage.appendInt(numHeaders);
-            }
+        boolean needAjpMessageHeader = true;
+        while (needAjpMessageHeader) {
+            // Write AJP message header
+            responseMessage.reset();
+            responseMessage.appendByte(Constants.JK_AJP13_SEND_HEADERS);
 
-            try {
-                // Write headers
-                MessageBytes hN = headers.getName(i);
-                int hC = Constants.getResponseAjpIndex(hN.toString());
-                if (hC > 0) {
-                    responseMessage.appendInt(hC);
-                } else {
-                    responseMessage.appendBytes(hN);
+            // Write HTTP response line
+            responseMessage.appendInt(statusCode);
+            // Reason phrase is optional but mod_jk + httpd 2.x fails with a null
+            // reason phrase - bug 45026
+            tmpMB.setString(Integer.toString(response.getStatus()));
+            responseMessage.appendBytes(tmpMB);
+
+            // Start headers
+            responseMessage.appendInt(numHeaders);
+
+            needAjpMessageHeader = false;
+
+            for (int i = 0; i < numHeaders; i++) {
+                try {
+                    // Write headers
+                    MessageBytes hN = headers.getName(i);
+                    int hC = Constants.getResponseAjpIndex(hN.toString());
+                    if (hC > 0) {
+                        responseMessage.appendInt(hC);
+                    } else {
+                        responseMessage.appendBytes(hN);
+                    }
+                    MessageBytes hV = headers.getValue(i);
+                    responseMessage.appendBytes(hV);
+                } catch (IllegalArgumentException iae) {
+                    // Log the problematic header
+                    log.warn(sm.getString("ajpprocessor.response.invalidHeader", headers.getName(i), headers.getValue(i)),
+                            iae);
+                    // Remove the problematic header
+                    headers.removeHeader(i);
+                    numHeaders--;
+                    // Restart writing of AJP message
+                    needAjpMessageHeader = true;
+                    break;
                 }
-                MessageBytes hV = headers.getValue(i);
-                responseMessage.appendBytes(hV);
-            } catch (IllegalArgumentException iae) {
-                // Log the problematic header
-                log.warn(sm.getString("ajpprocessor.response.invalidHeader", headers.getName(i), headers.getValue(i)),
-                        iae);
-                // Remove the problematic header
-                headers.removeHeader(i);
-                numHeaders--;
-                // Reset loop and start again
-                i = -1;
             }
         }
 
diff --git a/test/org/apache/coyote/ajp/TestAbstractAjpProcessor.java b/test/org/apache/coyote/ajp/TestAbstractAjpProcessor.java
index 111b033e851d..22b0466e6fb3 100644
--- a/test/org/apache/coyote/ajp/TestAbstractAjpProcessor.java
+++ b/test/org/apache/coyote/ajp/TestAbstractAjpProcessor.java
@@ -883,6 +883,60 @@ protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws Se
     }
 
 
+    /*
+     * https://bz.apache.org/bugzilla/show_bug.cgi?id=66591
+     */
+    @Test
+    public void testNoHeaders() throws Exception {
+
+        Tomcat tomcat = getTomcatInstance();
+
+        // No file system docBase required
+        Context ctx = tomcat.addContext("", null);
+
+        Tomcat.addServlet(ctx, "bug66591", new NoHeadersServlet());
+        ctx.addServletMappingDecoded("/", "bug66591");
+
+        tomcat.start();
+
+        SimpleAjpClient ajpClient = new SimpleAjpClient();
+        ajpClient.setPort(getPort());
+        ajpClient.connect();
+
+        validateCpong(ajpClient.cping());
+
+        TesterAjpMessage forwardMessage = ajpClient.createForwardMessage();
+        forwardMessage.end();
+
+        TesterAjpMessage responseHeaderMessage = ajpClient.sendMessage(forwardMessage, null);
+
+        // Expect 3 messages: headers, body chunk, end
+        Map<String, List<String>> responseHeaders = validateResponseHeaders(responseHeaderMessage, 200, "200");
+        Assert.assertTrue(responseHeaders.isEmpty());
+
+        String body = extractResponseBody(ajpClient.readMessage());
+        Assert.assertTrue(body.isEmpty());
+
+        validateResponseEnd(ajpClient.readMessage(), true);
+
+        // Double check the connection is still open
+        validateCpong(ajpClient.cping());
+
+        ajpClient.disconnect();
+    }
+
+
+    private static class NoHeadersServlet extends HttpServlet {
+
+        private static final long serialVersionUID = 1L;
+
+        @Override
+        protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
+            resp.flushBuffer();
+        }
+    }
+
+
     /**
      * Process response header packet and checks the status. Any other data is ignored.
      */
@@ -943,7 +997,7 @@ private String extractResponseBody(TesterAjpMessage message) throws Exception {
         Assert.assertEquals(0x03, message.readByte());
 
         int len = message.readInt();
-        Assert.assertTrue(len > 0);
+        Assert.assertTrue(len >= 0);
         return message.readString(len);
     }
 
diff --git a/webapps/docs/changelog.xml b/webapps/docs/changelog.xml
index 0de19ecbcd7c..89d263c6cf54 100644
--- a/webapps/docs/changelog.xml
+++ b/webapps/docs/changelog.xml
@@ -152,6 +152,11 @@
         <code>allowHostHeaderMismatch</code>. These are now hard-coded to the
         previous defaults. (markt)
       </update>
+      <fix>
+        <bug>66591</bug>: Fix a regression introduced in the fix for
+        <bug>66512</bug> that meant that an AJP Send Headers was not sent for
+        responses where no HTTP headers were set. (markt)
+      </fix>
     </changelog>
   </subsection>
   <subsection name="Jasper">