diff --git a/include/stream.h b/include/stream.h
index 8eaf8bf..68c7e71 100644
--- a/include/stream.h
+++ b/include/stream.h
@@ -23,6 +23,8 @@
 #include <stdint.h>
 #include <stdbool.h>
 
+#define STREAM_ALLOC_SIZE 4096
+
 enum stream_state {
 	STREAM_STATE_NORMAL = 0,
 	STREAM_STATE_CLOSED,
@@ -68,8 +70,6 @@ struct stream_impl {
 	void (*exec_and_send)(struct stream*, stream_exec_fn, void* userdata);
 };
 
-// TODO: Move some of these struct members into their respective implementation
-// classes.
 struct stream {
 	struct stream_impl *impl;
 
diff --git a/src/stream-gnutls.c b/src/stream-gnutls.c
index 416233d..2b7afb1 100644
--- a/src/stream-gnutls.c
+++ b/src/stream-gnutls.c
@@ -40,6 +40,9 @@ struct stream_gnutls {
 	gnutls_session_t session;
 };
 
+static_assert(sizeof(struct stream_gnutls) <= STREAM_ALLOC_SIZE,
+		"struct stream_gnutls has grown too large, increase STREAM_ALLOC_SIZE");
+
 static int stream__try_tls_accept(struct stream* self);
 
 static int stream_gnutls_close(struct stream* base)
diff --git a/src/stream-tcp.c b/src/stream-tcp.c
index 03a3d9b..eb94c1d 100644
--- a/src/stream-tcp.c
+++ b/src/stream-tcp.c
@@ -32,6 +32,9 @@
 #include "stream-common.h"
 #include "sys/queue.h"
 
+static_assert(sizeof(struct stream) <= STREAM_ALLOC_SIZE,
+		"struct stream has grown too large, increase STREAM_ALLOC_SIZE");
+
 static int stream_tcp_close(struct stream* self)
 {
 	if (self->state == STREAM_STATE_CLOSED)
@@ -255,7 +258,7 @@ static struct stream_impl impl = {
 
 struct stream* stream_new(int fd, stream_event_fn on_event, void* userdata)
 {
-	struct stream* self = calloc(1, sizeof(*self));
+	struct stream* self = calloc(1, STREAM_ALLOC_SIZE);
 	if (!self)
 		return NULL;