diff --git a/src/settings_test.c b/src/settings_test.c
index 1cd3fd7..80402b9 100644
--- a/src/settings_test.c
+++ b/src/settings_test.c
@@ -1,3 +1,5 @@
+#define _POSIX_C_SOURCE 200112L
+
 #include "settings.h"
 
 #include "acutest.h"
@@ -6,9 +8,6 @@
 
 #include <stdlib.h>
 
-// Not sure why this declaration isn't pulled in?
-extern int setenv(const char*, const char*, int);
-
 static void create_mock_languages_dir(const char* root, const char** dirs,
   int dirs_length) {
   mkdir(root, S_IRWXU | S_IRWXG | S_IROTH | S_IXOTH);