diff --git a/lib/client.c b/lib/client.c
index 1ba809b9..b4cd3361 100644
--- a/lib/client.c
+++ b/lib/client.c
@@ -707,10 +707,14 @@ check_extensions:
 
 			/* allow him to construct his ext instance */
 
-			ext->callback(lws_get_context(wsi), ext, wsi,
+			if (ext->callback(lws_get_context(wsi), ext, wsi,
 				      LWS_EXT_CB_CLIENT_CONSTRUCT,
 				      (void *)&wsi->act_ext_user[wsi->count_act_ext],
-				      (void *)&opts, 0);
+				      (void *)&opts, 0)) {
+				lwsl_notice(" ext %s failed construction\n", ext_name);
+				ext++;
+				continue;
+			}
 
 			/*
 			 * allow the user code to override ext defaults if it
diff --git a/lib/extension-permessage-deflate.c b/lib/extension-permessage-deflate.c
index 6ae348a6..439120af 100644
--- a/lib/extension-permessage-deflate.c
+++ b/lib/extension-permessage-deflate.c
@@ -75,6 +75,17 @@ lws_extension_callback_pm_deflate(struct lws_context *context,
 
 	case LWS_EXT_CB_CLIENT_CONSTRUCT:
 	case LWS_EXT_CB_CONSTRUCT:
+
+		n = LWS_MAX_SOCKET_IO_BUF;
+		if (wsi->protocol->rx_buffer_size)
+			n =  wsi->protocol->rx_buffer_size;
+
+		if (n < 128) {
+			lwsl_err(" permessage-deflate requires the protocol (%s) to have an RX buffer >= 128\n",
+					wsi->protocol->name);
+			return -1;
+		}
+
 		/* fill in **user */
 		priv = lws_zalloc(sizeof(*priv));
 		*((void **)user) = priv;
@@ -102,6 +113,23 @@ lws_extension_callback_pm_deflate(struct lws_context *context,
 		priv->args[PMD_TX_BUF_PWR2] = 10; /* ie, 1024 */
 		priv->args[PMD_COMP_LEVEL] = 1;
 		priv->args[PMD_MEM_LEVEL] = 8;
+
+		/* cap the RX buf at the nearest power of 2 to protocol rx buf */
+
+		n = LWS_MAX_SOCKET_IO_BUF;
+		if (wsi->protocol->rx_buffer_size)
+			n =  wsi->protocol->rx_buffer_size;
+
+		extra = 7;
+		while (n >= 1 << (extra + 1))
+			extra++;
+
+		if (extra < priv->args[PMD_RX_BUF_PWR2]) {
+			priv->args[PMD_RX_BUF_PWR2] = extra;
+			lwsl_err(" Capping pmd rx to %d\n", 1 << extra);
+		}
+		lwsl_err("   ok\n");
+
 		break;
 
 	case LWS_EXT_CB_DESTROY:
diff --git a/lib/server-handshake.c b/lib/server-handshake.c
index 5f525852..fd126a75 100644
--- a/lib/server-handshake.c
+++ b/lib/server-handshake.c
@@ -123,11 +123,6 @@ lws_extension_server_handshake(struct lws *wsi, char **p)
 
 			/* apply it */
 
-			if (ext_count)
-				*(*p)++ = ',';
-			else
-				LWS_CPYAPP(*p, "\x0d\x0aSec-WebSocket-Extensions: ");
-			*p += sprintf(*p, "%s", ext_name);
 			ext_count++;
 
 			/* instantiate the extension on this conn */
@@ -136,10 +131,21 @@ lws_extension_server_handshake(struct lws *wsi, char **p)
 
 			/* allow him to construct his context */
 
-			ext->callback(lws_get_context(wsi), ext, wsi,
+			if (ext->callback(lws_get_context(wsi), ext, wsi,
 				      LWS_EXT_CB_CONSTRUCT,
 				      (void *)&wsi->act_ext_user[wsi->count_act_ext],
-				      NULL, 0);
+				      NULL, 0)) {
+				lwsl_notice("ext %s failed construction\n", ext_name);
+				ext_count--;
+				ext++;
+				continue;
+			}
+
+			if (ext_count > 1)
+				*(*p)++ = ',';
+			else
+				LWS_CPYAPP(*p, "\x0d\x0aSec-WebSocket-Extensions: ");
+			*p += sprintf(*p, "%s", ext_name);
 
 			wsi->count_act_ext++;
 			lwsl_parser("count_act_ext <- %d\n", wsi->count_act_ext);
diff --git a/test-server/test-server.c b/test-server/test-server.c
index 09f70464..8fabc825 100644
--- a/test-server/test-server.c
+++ b/test-server/test-server.c
@@ -89,25 +89,25 @@ static struct lws_protocols protocols[] = {
 		"dumb-increment-protocol",
 		callback_dumb_increment,
 		sizeof(struct per_session_data__dumb_increment),
-		10,
+		10, /* rx buf size must be >= permessage-deflate rx size */
 	},
 	{
 		"lws-mirror-protocol",
 		callback_lws_mirror,
 		sizeof(struct per_session_data__lws_mirror),
-		128,
+		128, /* rx buf size must be >= permessage-deflate rx size */
 	},
 	{
 		"lws-echogen",
 		callback_lws_echogen,
 		sizeof(struct per_session_data__echogen),
-		128,
+		128, /* rx buf size must be >= permessage-deflate rx size */
 	},
 	{
 		"lws-status",
 		callback_lws_status,
 		sizeof(struct per_session_data__lws_status),
-		128,
+		128, /* rx buf size must be >= permessage-deflate rx size */
 	},
 	{ NULL, NULL, 0, 0 } /* terminator */
 };
diff --git a/test-server/test.html b/test-server/test.html
index eff2ba19..450a296b 100644
--- a/test-server/test.html
+++ b/test-server/test.html
@@ -127,6 +127,7 @@ to zero just this connection's number.
 	    <td align=center><div id=number style="font-size:120%;"> </div></td>
 	    <td align=center>
 	     <input type=button id=offset value="Reset counter" onclick="reset();" >
+	     <input type=button id=junk value="Send junk" onclick="junk();" >
 	    </td>
 	    </tr>
 	 </table>
@@ -477,7 +478,7 @@ document.getElementById("number").textContent = get_appropriate_ws_url();
 			document.getElementById("s_statustd").style.backgroundColor = "#40ff40";
 			document.getElementById("s_status").innerHTML =
 				" <b>websocket connection opened</b><br>" +
-				san(socket_di.extensions);
+				san(socket_status.extensions);
 		} 
 
 		socket_status.onmessage =function got_packet(msg) {
@@ -514,6 +515,12 @@ function reset() {
 	socket_di.send("reset\n");
 }
 
+
+function junk() {
+	for(var word = ''; word.length < 9000; word += 'a'){}
+	socket_di.send(word);
+}
+
 var socket_ot;
 
 function ot_open() {
@@ -579,7 +586,7 @@ function ot_req_close() {
 			document.getElementById("wslm_statustd").style.backgroundColor = "#40ff40";
 			document.getElementById("wslm_status").innerHTML =
 				" <b>websocket connection opened</b><br>" +
-				san(socket_di.extensions);
+				san(socket_lm.extensions);
 		} 
 
 		socket_lm.onmessage =function got_packet(msg) {