diff --git a/tools/lint/common.c b/tools/lint/common.c
index bc4d572..16e05d1 100644
--- a/tools/lint/common.c
+++ b/tools/lint/common.c
@@ -13,6 +13,7 @@
  */
 
 #define _GNU_SOURCE
+#define _POSIX_C_SOURCE 200809L /* strdup, strndup */
 
 #include "common.h"
 
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>
diff --git a/tools/lint/linenoise/linenoise.c b/tools/lint/linenoise/linenoise.c
index f14d348..dd81e74 100644
--- a/tools/lint/linenoise/linenoise.c
+++ b/tools/lint/linenoise/linenoise.c
@@ -106,6 +106,7 @@
  */
 
 #define _GNU_SOURCE
+#define _POSIX_C_SOURCE 200809L /* strdup */
 
 #include "linenoise.h"
 
diff --git a/tools/lint/main.c b/tools/lint/main.c
index ebbd7f8..44eca9b 100644
--- a/tools/lint/main.c
+++ b/tools/lint/main.c
@@ -13,6 +13,7 @@
  */
 
 #define _GNU_SOURCE
+#define _POSIX_C_SOURCE 200809L /* strdup */
 
 #include <stdint.h>
 #include <stdio.h>
diff --git a/tools/re/main.c b/tools/re/main.c
index c8d066f..8583e73 100644
--- a/tools/re/main.c
+++ b/tools/re/main.c
@@ -13,6 +13,7 @@
  */
 
 #define _GNU_SOURCE
+#define _POSIX_C_SOURCE 200809L /* strdup, getline */
 
 #include <errno.h>
 #include <getopt.h>