diff --git a/mfshell/commands/put.c b/mfshell/commands/put.c
index 5919f78..6495398 100644
--- a/mfshell/commands/put.c
+++ b/mfshell/commands/put.c
@@ -17,6 +17,7 @@
  */
 
 #define _POSIX_C_SOURCE 200809L // for PATH_MAX
+#define _GNU_SOURCE             // for strdup
 
 #include <stdio.h>
 #include <stdlib.h>