diff -uw -r a/src/flexdef.h b/src/flexdef.h
--- a/src/flexdef.h	2017-05-03 11:13:14.000000000 -0700
+++ b/src/flexdef.h	2019-10-30 13:20:37.611169753 -0700
@@ -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>