diff --git a/ssl/dtls1.h b/ssl/dtls1.h
index 2900d1d8a..f85acf59d 100644
--- a/ssl/dtls1.h
+++ b/ssl/dtls1.h
@@ -57,8 +57,14 @@
  *
  */
 
-#ifndef HEADER_DTLS1_H 
-#define HEADER_DTLS1_H 
+#ifndef HEADER_DTLS1_H
+#define HEADER_DTLS1_H
+
+/* Unless _XOPEN_SOURCE_EXTENDED is defined, struct timeval will not be
+   properly defined with DEC C, at least on VMS */
+#if defined(__DECC) || defined(__DECCXX)
+#define _XOPEN_SOURCE_EXTENDED
+#endif
 
 #include <openssl/buffer.h>
 #include <openssl/pqueue.h>