diff --git a/tools/lint/completion.c b/tools/lint/completion.c
index 4db17a0..2506019 100644
--- a/tools/lint/completion.c
+++ b/tools/lint/completion.c
@@ -13,6 +13,7 @@
  */
 
 #define _GNU_SOURCE
+#define _POSIX_C_SOURCE 200809L /* strdup */
 
 #include <errno.h>
 #include <stdint.h>