diff --git a/fat-arm.c b/fat-arm.c
index 1156499d6e908f107501607ecb99c7a769d9e822..d52b1439f2d88991c26b5a4b00f76ff45a8203df 100644
--- a/fat-arm.c
+++ b/fat-arm.c
@@ -29,6 +29,8 @@
    not, see http://www.gnu.org/licenses/.
 */
 
+#define _GNU_SOURCE
+
 #if HAVE_CONFIG_H
 # include "config.h"
 #endif