diff --git a/src/eport.c b/src/eport.c
index 7dac4c9..29cc237 100644
--- a/src/eport.c
+++ b/src/eport.c
@@ -55,7 +55,7 @@ ssize_t eport_read(FILE *stream, char *buffer, size_t buffer_size)
 ssize_t eport_write(FILE *stream, char *buffer, size_t buffer_size)
 {
   int fd = fileno(stream);
-  int16_t port_msg_len = (buffer_size << 8) | ((buffer_size >> 8) & 0xFF);
+  int16_t port_msg_len = ((int16_t)buffer_size << 8) | (((int16_t)buffer_size >> 8) & 0xFF);
   ssize_t wr = 0;
   struct iovec msg[2];