diff --git a/crypto/dh/dh.h b/crypto/dh/dh.h
index 62dba4055c7fc84e7ec77fa276c2684546ad0906..db4e11090db403f2154becb0c54e01be11bd640c 100644
--- a/crypto/dh/dh.h
+++ b/crypto/dh/dh.h
@@ -59,6 +59,8 @@
 #ifndef HEADER_DH_H
 #define HEADER_DH_H
 
+#include <openssl/e_os2.h>
+
 #ifdef OPENSSL_NO_DH
 #error DH is disabled.
 #endif