diff --git a/xs/src/admesh/stl_io.c b/xs/src/admesh/stl_io.c
index daa999b8d..95dff856e 100644
--- a/xs/src/admesh/stl_io.c
+++ b/xs/src/admesh/stl_io.c
@@ -249,7 +249,7 @@ stl_write_binary(stl_file *stl, const char *file, const char *label)
 
   
   /* Open the file */
-  fp = fopen(file, "w");
+  fp = fopen(file, "wb");
   if(fp == NULL)
     {
       error_msg = (char*)