diff --git a/lib/client.c b/lib/client.c
index 5afd8eab..fb0c0671 100644
--- a/lib/client.c
+++ b/lib/client.c
@@ -767,6 +767,7 @@ check_accept:
 		lwsl_err("Out of Mem allocating rx buffer %d\n", n);
 		goto bail2;
 	}
+       wsi->u.ws.rx_ubuf_alloc = n;
 	lwsl_info("Allocating client RX buffer %d\n", n);
 
 	if (setsockopt(wsi->sock, SOL_SOCKET, SO_SNDBUF, (const char *)&n, sizeof n)) {
diff --git a/lib/parsers.c b/lib/parsers.c
index b660b38e..aa99a44e 100644
--- a/lib/parsers.c
+++ b/lib/parsers.c
@@ -820,6 +820,10 @@ handle_first:
 			return 1;
 		}
 
+               if (wsi->u.ws.rx_ubuf_head + LWS_PRE >= wsi->u.ws.rx_ubuf_alloc) {
+                       lwsl_err("Attempted overflow\n");
+                       return -1;
+               }
 		if (wsi->u.ws.all_zero_nonce)
 			wsi->u.ws.rx_user_buffer[LWS_SEND_BUFFER_PRE_PADDING +
 			       (wsi->u.ws.rx_user_buffer_head++)] = c;
diff --git a/lib/private-libwebsockets.h b/lib/private-libwebsockets.h
index c9c69968..45bb563c 100644
--- a/lib/private-libwebsockets.h
+++ b/lib/private-libwebsockets.h
@@ -776,6 +776,7 @@ struct _lws_header_related {
 struct _lws_websocket_related {
 	char *rx_user_buffer;
 	int rx_user_buffer_head;
+	unsigned int rx_ubuf_alloc;
 	unsigned char frame_masking_nonce_04[4];
 	unsigned char frame_mask_index;
 	size_t rx_packet_length;
diff --git a/lib/server.c b/lib/server.c
index b98bf1e9..e987042a 100644
--- a/lib/server.c
+++ b/lib/server.c
@@ -561,6 +561,7 @@ upgrade_ws:
 			lwsl_err("Out of Mem allocating rx buffer %d\n", n);
 			return 1;
 		}
+		wsi->u.ws.rx_ubuf_alloc = n;
 		lwsl_info("Allocating RX buffer %d\n", n);
 
 		if (setsockopt(wsi->sock, SOL_SOCKET, SO_SNDBUF, (const char *)&n, sizeof n)) {