diff --git a/crypto/o_str.c b/crypto/o_str.c
index 5cdfc4f9a0..42b25d078f 100644
--- a/crypto/o_str.c
+++ b/crypto/o_str.c
@@ -56,7 +56,9 @@
  *
  */
 
-#include <o_str.h>
+#include <ctype.h>
+#include <strings.h>
+#include "o_str.h"
 #include <openssl/e_os2.h>
 
 #undef strncasecmp