diff --git a/src/xxd/xxd.c b/src/xxd/xxd.c
index cf2a356..c32b9b8 100644
--- a/src/xxd/xxd.c
+++ b/src/xxd/xxd.c
@@ -72,6 +72,10 @@
 # define CYGWIN
 #endif
 
+#if (defined(__linux__) && !defined(__ANDROID__)) || defined(__CYGWIN__)
+# define _XOPEN_SOURCE 700   /* for fdopen() */
+#endif
+
 #include <stdio.h>
 #ifdef VAXC
 # include <file.h>