diff --git a/lib/dns/master.c b/lib/dns/master.c
index 463ee5241a..ff1c2abbe9 100644
--- a/lib/dns/master.c
+++ b/lib/dns/master.c
@@ -773,7 +773,7 @@ static isc_result_t
 openfile_raw(dns_loadctx_t *lctx, const char *master_file) {
 	isc_result_t result;
 
-	result = isc_stdio_open(master_file, "r", &lctx->f);
+	result = isc_stdio_open(master_file, "rb", &lctx->f);
 	if (result != ISC_R_SUCCESS && result != ISC_R_FILENOTFOUND) {
 		UNEXPECTED_ERROR(__FILE__, __LINE__,
 				 "isc_stdio_open() failed: %s",