diff --git a/lib/client.c b/lib/client.c
index d9a1af37..af80e276 100644
--- a/lib/client.c
+++ b/lib/client.c
@@ -751,6 +751,7 @@ 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,
diff --git a/lib/parsers.c b/lib/parsers.c
index 18037d0d..e08f4f6c 100644
--- a/lib/parsers.c
+++ b/lib/parsers.c
@@ -885,6 +885,10 @@ handle_first:
 			return 1;
 		}
 
+               if (wsi->u.ws.rx_user_buffer_head + LWS_SEND_BUFFER_PRE_PADDING >= 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 62a3646d..a8277f02 100644
--- a/lib/private-libwebsockets.h
+++ b/lib/private-libwebsockets.h
@@ -818,6 +818,7 @@ struct _lws_websocket_related {
 	unsigned int rx_user_buffer_head;
 	unsigned char mask_nonce[4];
 	unsigned char frame_mask_index;
+	unsigned int rx_ubuf_alloc;
 	size_t rx_packet_length;
 	unsigned char opcode;
 	unsigned int final:1;
diff --git a/lib/server.c b/lib/server.c
index 7e728f36..e3e8ef74 100644
--- a/lib/server.c
+++ b/lib/server.c
@@ -566,6 +566,7 @@ 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 LWS_POSIX
 		if (setsockopt(wsi->sock, SOL_SOCKET, SO_SNDBUF,