diff --git a/cpu/x86/mtarch.h b/cpu/x86/mtarch.h
index 3a1fefa3f..fe9da7ec6 100644
--- a/cpu/x86/mtarch.h
+++ b/cpu/x86/mtarch.h
@@ -1,19 +1,19 @@
 /*
  * Copyright (c) 2003, Adam Dunkels.
- * All rights reserved. 
+ * All rights reserved.
  *
- * Redistribution and use in source and binary forms, with or without 
- * modification, are permitted provided that the following conditions 
- * are met: 
- * 1. Redistributions of source code must retain the above copyright 
- *    notice, this list of conditions and the following disclaimer. 
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above
  *    copyright notice, this list of conditions and the following
  *    disclaimer in the documentation and/or other materials provided
- *    with the distribution. 
+ *    with the distribution.
  * 3. The name of the author may not be used to endorse or promote
  *    products derived from this software without specific prior
- *    written permission.  
+ *    written permission.
  *
  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS
  * OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
@@ -25,13 +25,15 @@
  * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
  * WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
  * NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
- * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.  
+ * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  *
  */
 #ifndef __MTARCH_H__
 #define __MTARCH_H__
 
+#ifndef MTARCH_STACKSIZE
 #define MTARCH_STACKSIZE 1024
+#endif /* MTARCH_STACKSIZE */
 
 struct mtarch_thread {
   /* Note: stack must be aligned on 4-byte boundary. */