diff --git a/e_os.h b/e_os.h
index 2147c17052208adb260988443f89ffc28d8fd443..1e06e0a2fe50eec3b6c39ca952ac6e9920c21993 100644
--- a/e_os.h
+++ b/e_os.h
@@ -266,6 +266,9 @@ extern "C" {
 #    ifndef NO_SYS_TYPES_H
 #      include <sys/types.h>
 #    endif
+#    ifdef NeXT
+#      define pid_t int /* pid_t is missing on NEXTSTEP/OPENSTEP */
+#    endif
 
 #    define OPENSSL_CONF	"openssl.cnf"
 #    define SSLEAY_CONF		OPENSSL_CONF