diff --git a/src/mod_fastcgi.c b/src/mod_fastcgi.c
index d5831c2a..12076007 100644
--- a/src/mod_fastcgi.c
+++ b/src/mod_fastcgi.c
@@ -217,9 +217,7 @@ static handler_t fcgi_create_env(server *srv, handler_ctx *hctx) {
 	FCGI_Header header;
 	int request_id;
 
-	buffer *b = chunkqueue_prepend_buffer_open(hctx->wb);
 	gw_host *host = hctx->host;
-
 	connection *con   = hctx->remote_conn;
 
 	http_cgi_opts opts = {
@@ -229,6 +227,8 @@ static handler_t fcgi_create_env(server *srv, handler_ctx *hctx) {
 	  host->strip_request_uri
 	};
 
+	buffer * const b = chunkqueue_prepend_buffer_open_sz(hctx->wb, (size_t)(con->read_queue->bytes_out - hctx->wb->bytes_in));
+
 	/* send FCGI_BEGIN_REQUEST */
 
 	if (hctx->request_id == 0) {
@@ -245,10 +245,6 @@ static handler_t fcgi_create_env(server *srv, handler_ctx *hctx) {
 	beginRecord.body.flags = 0;
 	memset(beginRecord.body.reserved, 0, sizeof(beginRecord.body.reserved));
 
-	if ((off_t)buffer_string_space(b) < con->read_queue->bytes_out - hctx->wb->bytes_in) {
-		buffer_string_prepare_copy(b, ((size_t)(con->read_queue->bytes_out - hctx->wb->bytes_in + 4095) & ~4095uL)-1);
-	}
-
 	buffer_copy_string_len(b, (const char *)&beginRecord, sizeof(beginRecord));
 	fcgi_header(&header, FCGI_PARAMS, request_id, 0, 0); /*(set aside space to fill in later)*/
 	buffer_append_string_len(b, (const char *)&header, sizeof(header));
diff --git a/src/mod_proxy.c b/src/mod_proxy.c
index 97b82117..f43c0d8e 100644
--- a/src/mod_proxy.c
+++ b/src/mod_proxy.c
@@ -708,15 +708,11 @@ static void proxy_set_Forwarded(connection *con, const unsigned int flags) {
 static handler_t proxy_create_env(server *srv, gw_handler_ctx *gwhctx) {
 	handler_ctx *hctx = (handler_ctx *)gwhctx;
 	connection *con = hctx->gw.remote_conn;
-	buffer *b = chunkqueue_prepend_buffer_open(hctx->gw.wb);
 	const int remap_headers = (NULL != hctx->conf.header.urlpaths
 				   || NULL != hctx->conf.header.hosts_request);
 	const int upgrade = hctx->conf.header.upgrade
 	    && (NULL != http_header_request_get(con, HTTP_HEADER_UPGRADE, CONST_STR_LEN("Upgrade")));
-
-	if ((off_t)buffer_string_space(b) < con->read_queue->bytes_out - hctx->gw.wb->bytes_in) {
-		buffer_string_prepare_copy(b, ((size_t)(con->read_queue->bytes_out - hctx->gw.wb->bytes_in + 4095) & ~4095uL)-1);
-	}
+	buffer * const b = chunkqueue_prepend_buffer_open_sz(hctx->gw.wb, (size_t)(con->read_queue->bytes_out - hctx->gw.wb->bytes_in));
 
 	/* build header */
 
diff --git a/src/mod_scgi.c b/src/mod_scgi.c
index abd19626..bc40ee7b 100644
--- a/src/mod_scgi.c
+++ b/src/mod_scgi.c
@@ -156,7 +156,6 @@ static int scgi_env_add_uwsgi(void *venv, const char *key, size_t key_len, const
 
 
 static handler_t scgi_create_env(server *srv, handler_ctx *hctx) {
-	buffer *b = chunkqueue_prepend_buffer_open(hctx->wb);
 	gw_host *host = hctx->host;
 	connection *con = hctx->remote_conn;
 	http_cgi_opts opts = { 0, 0, host->docroot, NULL };
@@ -164,10 +163,7 @@ static handler_t scgi_create_env(server *srv, handler_ctx *hctx) {
 	  ? scgi_env_add_scgi
 	  : scgi_env_add_uwsgi;
 	size_t offset;
-
-	if ((off_t)buffer_string_space(b) < con->read_queue->bytes_out - hctx->wb->bytes_in) {
-		buffer_string_prepare_copy(b, ((size_t)(con->read_queue->bytes_out - hctx->wb->bytes_in + 4095) & ~4095uL)-1);
-	}
+	buffer * const b = chunkqueue_prepend_buffer_open_sz(hctx->wb, (size_t)(con->read_queue->bytes_out - hctx->wb->bytes_in));
 
         /* save space for 9 digits (plus ':'), though incoming HTTP request
 	 * currently limited to 64k (65535, so 5 chars) */