diff -Naur flex-2.6.4.orig/src/flexdef.h flex-2.6.4/src/flexdef.h
--- flex-2.6.4.orig/src/flexdef.h	2017-05-03 14:13:14.000000000 -0400
+++ flex-2.6.4/src/flexdef.h	2020-05-30 01:17:52.823015929 -0400
@@ -47,6 +47,7 @@
 #include <libgen.h> /* for XPG version of basename(3) */
 #include <string.h>
 #include <math.h>
+#include <malloc.h>
 
 #ifdef HAVE_ASSERT_H
 #include <assert.h>