diff --git a/bin/otpkey/otpkey.c b/bin/otpkey/otpkey.c
index e315e2c..b208e47 100644
--- a/bin/otpkey/otpkey.c
+++ b/bin/otpkey/otpkey.c
@@ -27,7 +27,7 @@
  * SUCH DAMAGE.
  */
 
-#include "cryb/otp-impl.h"
+#include "cryb/impl.h"
 
 #include <stdio.h>
 #include <stdlib.h>
diff --git a/include/cryb/Makefile.am b/include/cryb/Makefile.am
index d8f825e..fb4466c 100644
--- a/include/cryb/Makefile.am
+++ b/include/cryb/Makefile.am
@@ -7,4 +7,4 @@ cryb_HEADERS += otp.h
 endif OTP_LIB
 
 noinst_HEADERS = \
-	otp-impl.h
+	impl.h
diff --git a/include/cryb/otp-impl.h b/include/cryb/impl.h
similarity index 93%
rename from include/cryb/otp-impl.h
rename to include/cryb/impl.h
index 459132c..dbf32da 100644
--- a/include/cryb/otp-impl.h
+++ b/include/cryb/impl.h
@@ -1,5 +1,5 @@
 /*-
- * Copyright (c) 2017 Dag-Erling Smørgrav
+ * Copyright (c) 2014-2016 Dag-Erling Smørgrav
  * All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
@@ -27,8 +27,8 @@
  * SUCH DAMAGE.
  */
 
-#ifndef CRYB_OTP_IMPL_H_INCLUDED
-#define CRYB_OTP_IMPL_H_INCLUDED
+#ifndef CRYB_IMPL_H_INCLUDED
+#define CRYB_IMPL_H_INCLUDED
 
 #if HAVE_CONFIG_H
 #include "config.h"
diff --git a/lib/otp/cryb_otp.c b/lib/otp/cryb_otp.c
index 91752a2..bbf491a 100644
--- a/lib/otp/cryb_otp.c
+++ b/lib/otp/cryb_otp.c
@@ -27,7 +27,7 @@
  * SUCH DAMAGE.
  */
 
-#include "cryb/otp-impl.h"
+#include "cryb/impl.h"
 
 #include <stdint.h>
 #include <unistd.h>
diff --git a/libexec/login_otp/login_otp.c b/libexec/login_otp/login_otp.c
index 5d3587e..4de4b5a 100644
--- a/libexec/login_otp/login_otp.c
+++ b/libexec/login_otp/login_otp.c
@@ -27,7 +27,7 @@
  * SUCH DAMAGE.
  */
 
-#include "cryb/otp-impl.h"
+#include "cryb/impl.h"
 
 #include <stdio.h>
 #include <stdlib.h>
diff --git a/pam/pam_otp/pam_otp.c b/pam/pam_otp/pam_otp.c
index c60752e..5631b36 100644
--- a/pam/pam_otp/pam_otp.c
+++ b/pam/pam_otp/pam_otp.c
@@ -27,7 +27,7 @@
  * SUCH DAMAGE.
  */
 
-#include "cryb/otp-impl.h"
+#include "cryb/impl.h"
 
 #define PAM_SM_AUTH
 
diff --git a/sbin/otpradiusd/otpradiusd.c b/sbin/otpradiusd/otpradiusd.c
index 9e5fa92..491ec3c 100644
--- a/sbin/otpradiusd/otpradiusd.c
+++ b/sbin/otpradiusd/otpradiusd.c
@@ -27,7 +27,7 @@
  * SUCH DAMAGE.
  */
 
-#include "cryb/otp-impl.h"
+#include "cryb/impl.h"
 
 #include <stdio.h>
 #include <stdlib.h>
diff --git a/t/t_cxx.cc b/t/t_cxx.cc
index 8203b53..69fbc02 100644
--- a/t/t_cxx.cc
+++ b/t/t_cxx.cc
@@ -27,7 +27,7 @@
  * SUCH DAMAGE.
  */
 
-#include "cryb/otp-impl.h"
+#include "cryb/impl.h"
 
 /* gcc's <cstdint> is broken */
 #include <stdint.h>