diff --git a/tests/stdio/printf.c b/tests/stdio/printf.c
index 49e6905933..073a609ca4 100644
--- a/tests/stdio/printf.c
+++ b/tests/stdio/printf.c
@@ -1,4 +1,5 @@
 #include <stdio.h>
+#include <stdlib.h> // free()
 #include <math.h> // INFINITY, NAN constants
 
 int main(void) {