diff --git a/libserialport.h.in b/libserialport.h.in
index 51d9afe..6a09318 100644
--- a/libserialport.h.in
+++ b/libserialport.h.in
@@ -108,7 +108,9 @@ enum sp_mode {
 	/** Open port for read access. */
 	SP_MODE_READ = 1,
 	/** Open port for write access. */
-	SP_MODE_WRITE = 2
+	SP_MODE_WRITE = 2,
+	/** Open port for read and write access. */
+	SP_MODE_READ_WRITE = 3
 };
 
 /** Port events. */
diff --git a/serialport.c b/serialport.c
index 4dc1b83..d437140 100644
--- a/serialport.c
+++ b/serialport.c
@@ -402,7 +402,7 @@ SP_API enum sp_return sp_open(struct sp_port *port, enum sp_mode flags)
 
 	CHECK_PORT();
 
-	if (flags > (SP_MODE_READ | SP_MODE_WRITE))
+	if (flags > SP_MODE_READ_WRITE)
 		RETURN_ERROR(SP_ERR_ARG, "Invalid flags");
 
 	DEBUG_FMT("Opening port %s", port->name);
@@ -479,7 +479,7 @@ SP_API enum sp_return sp_open(struct sp_port *port, enum sp_mode flags)
 	int flags_local = O_NONBLOCK | O_NOCTTY;
 
 	/* Map 'flags' to the OS-specific settings. */
-	if (flags & (SP_MODE_READ | SP_MODE_WRITE))
+	if ((flags & SP_MODE_READ_WRITE) == SP_MODE_READ_WRITE)
 		flags_local |= O_RDWR;
 	else if (flags & SP_MODE_READ)
 		flags_local |= O_RDONLY;