diff --git a/src/fileio.c b/src/fileio.c
index 9c3313b2..79fccd5c 100644
--- a/src/fileio.c
+++ b/src/fileio.c
@@ -1335,7 +1335,7 @@ int fileio_fmt_autodetect(const char * fname)
   int found;
   int first = 1;
 
-#if defined(WIN32)
+#if !defined(WIN32)
   f = fopen(fname, "r");
 #else
   f = fopen(fname, "rb");