diff --git a/src/generator.c b/src/generator.c
index 4dc48d36..e40b920d 100644
--- a/src/generator.c
+++ b/src/generator.c
@@ -771,6 +771,9 @@ static bool passthrough_stratum(connsock_t *cs, proxy_instance_t *proxi)
 	JSON_CPACK(req, "{s:s,s:[s]}",
 			"method", "mining.passthrough",
 			"params", PACKAGE"/"VERSION);
+
+	/* Serialise all send/recvs */
+	cksem_wait(&cs->sem);
 	ret = send_json_msg(cs, req);
 	json_decref(req);
 	if (!ret) {
@@ -796,6 +799,8 @@ static bool passthrough_stratum(connsock_t *cs, proxy_instance_t *proxi)
 	}
 	proxi->passthrough = true;
 out:
+	cksem_post(&cs->sem);
+
 	if (val)
 		json_decref(val);
 	if (!ret)
@@ -1771,6 +1776,9 @@ static bool proxy_alive(ckpool_t *ckp, proxy_instance_t *proxi, connsock_t *cs,
 		return true;
 	if (proxi->disabled)
 		return false;
+
+	/* Serialise all send/recvs here with the cs semaphore */
+	cksem_wait(&cs->sem);
 	if (!extract_sockaddr(proxi->url, &cs->url, &cs->port)) {
 		LOGWARNING("Failed to extract address from %s", proxi->url);
 		goto out;
@@ -1810,6 +1818,8 @@ static bool proxy_alive(ckpool_t *ckp, proxy_instance_t *proxi, connsock_t *cs,
 	}
 	proxi->authorised = ret = true;
 out:
+	cksem_post(&cs->sem);
+
 	if (!ret) {
 		send_stratifier_deadproxy(ckp, proxi->id, proxi->subid);
 		/* Close and invalidate the file handle */
@@ -1937,7 +1947,10 @@ static void *passthrough_recv(void *arg)
 		}
 
 		/* Make sure we receive a line within 90 seconds */
+		cksem_wait(&cs->sem);
 		ret = read_socket_line(cs, &timeout);
+		cksem_post(&cs->sem);
+
 		if (ret < 1) {
 			reconnect_generator(ckp);
 			LOGWARNING("Proxy %d:%s failed to read_socket_line in passthrough_recv, attempting reconnect",
@@ -2048,12 +2061,17 @@ static void *proxy_recv(void *arg)
 		}
 		mutex_unlock(&gdata->share_lock);
 
+		cs = NULL;
 		/* If we don't get an update within 10 minutes the upstream pool
 		 * has likely stopped responding. */
 		ret = epoll_wait(epfd, &event, 1, 600000);
 		if (likely(ret > 0)) {
 			subproxy = event.data.ptr;
 			cs = &subproxy->cs;
+
+			/* Serialise messages from here once we have a cs by
+			 * holding the semaphore. */
+			cksem_wait(&cs->sem);
 			if (event.events & (EPOLLHUP | EPOLLERR | EPOLLRDHUP))
 				ret = -1;
 			else {
@@ -2065,9 +2083,7 @@ static void *proxy_recv(void *arg)
 			LOGNOTICE("Proxy %d:%d %s failed to epoll/read_socket_line in proxy_recv",
 				  proxi->id, subproxy->subid, subproxy->url);
 			disable_subproxy(gdata, proxi, subproxy);
-			continue;
-		}
-		do {
+		} else do {
 			/* subproxy may have been recycled here if it is not a
 			 * parent and reconnect was issued */
 			if (parse_method(ckp, subproxy, cs->buf))
@@ -2079,6 +2095,8 @@ static void *proxy_recv(void *arg)
 			}
 			timeout = 0;
 		} while ((ret = read_socket_line(cs, &timeout)) > 0);
+		if (cs)
+			cksem_post(&cs->sem);
 	}
 
 	return NULL;
@@ -2132,7 +2150,6 @@ static void *userproxy_recv(void *arg)
 		if (unlikely(!proxy->authorised))
 			continue;
 
-		cs = &proxy->cs;
 		if (event.events & (EPOLLHUP | EPOLLERR | EPOLLRDHUP)) {
 			LOGNOTICE("Proxy %d:%d %s hung up in epoll_wait", proxy->id,
 				  proxy->subid, proxy->url);
@@ -2162,6 +2179,9 @@ static void *userproxy_recv(void *arg)
 		mutex_unlock(&gdata->share_lock);
 
 		timeout = 0;
+		cs = &proxy->cs;
+
+		cksem_wait(&cs->sem);
 		while ((ret = read_socket_line(cs, &timeout)) > 0) {
 			/* proxy may have been recycled here if it is not a
 			 * parent and reconnect was issued */
@@ -2174,6 +2194,7 @@ static void *userproxy_recv(void *arg)
 			}
 			timeout = 0;
 		}
+		cksem_post(&cs->sem);
 	}
 	return NULL;
 }
@@ -2811,6 +2832,8 @@ static proxy_instance_t *__add_proxy(ckpool_t *ckp, gdata_t *gdata, const int id
 	proxy->ckp = proxy->cs.ckp = ckp;
 	HASH_ADD_INT(gdata->proxies, id, proxy);
 	proxy->global = true;
+	cksem_init(&proxy->cs.sem);
+	cksem_post(&proxy->cs.sem);
 	return proxy;
 }