diff --git a/src/serial_posix.c b/src/serial_posix.c
index 352655b..6f2ae71 100644
--- a/src/serial_posix.c
+++ b/src/serial_posix.c
@@ -691,7 +691,7 @@ dc_serial_read (dc_iostream_t *abstract, void *data, size_t size, size_t *actual
 
 			if (init) {
 				// Calculate the initial timeout.
-				timeout = device->timeout * 1000;
+				timeout = (dc_usecs_t) device->timeout * 1000;
 				// Calculate the target time.
 				target = now + timeout;
 				init = 0;