diff --git a/src/openvpn/crypto.c b/src/openvpn/crypto.c
index 6d34acd..b1d6780 100644
--- a/src/openvpn/crypto.c
+++ b/src/openvpn/crypto.c
@@ -722,7 +722,7 @@ crypto_adjust_frame_parameters(struct frame *frame,
 
     crypto_overhead += kt->hmac_length;
 
-    frame_add_to_extra_frame(frame, crypto_overhead);
+    frame_add_to_extra_frame(frame, (unsigned int) crypto_overhead);
 
     msg(D_MTU_DEBUG, "%s: Adjusting frame parameters for crypto by %u bytes",
         __func__, (unsigned int) crypto_overhead);
diff --git a/src/openvpn/init.c b/src/openvpn/init.c
index 52c64da..fe70175 100644
--- a/src/openvpn/init.c
+++ b/src/openvpn/init.c
@@ -2675,7 +2675,7 @@ do_init_crypto_tls(struct context *c, const unsigned int flags)
     if (c->options.pull || c->options.mode == MODE_SERVER)
     {
         /* Account for worst-case crypto overhead before allocating buffers */
-        frame_add_to_extra_frame(&c->c2.frame, crypto_max_overhead());
+        frame_add_to_extra_frame(&c->c2.frame, (unsigned int) crypto_max_overhead());
     }
     else
     {
diff --git a/src/openvpn/mtu.h b/src/openvpn/mtu.h
index a82154a..690eb81 100644
--- a/src/openvpn/mtu.h
+++ b/src/openvpn/mtu.h
@@ -271,12 +271,18 @@ frame_add_to_link_mtu(struct frame *frame, const int increment)
 }
 
 static inline void
-frame_add_to_extra_frame(struct frame *frame, const int increment)
+frame_add_to_extra_frame(struct frame *frame, const unsigned int increment)
 {
     frame->extra_frame += increment;
 }
 
 static inline void
+frame_remove_from_extra_frame(struct frame *frame, const unsigned int increment)
+{
+    frame->extra_frame -= increment;
+}
+
+static inline void
 frame_add_to_extra_tun(struct frame *frame, const int increment)
 {
     frame->extra_tun += increment;
diff --git a/src/openvpn/options.c b/src/openvpn/options.c
index e42029c..be47090 100644
--- a/src/openvpn/options.c
+++ b/src/openvpn/options.c
@@ -3509,7 +3509,7 @@ calc_options_string_link_mtu(const struct options *o, const struct frame *frame)
         struct key_type fake_kt;
         init_key_type(&fake_kt, o->ciphername, o->authname, o->keysize, true,
                       false);
-        frame_add_to_extra_frame(&fake_frame, -(crypto_max_overhead()));
+        frame_remove_from_extra_frame(&fake_frame, (unsigned int) crypto_max_overhead());
         crypto_adjust_frame_parameters(&fake_frame, &fake_kt, o->replay,
                                        cipher_kt_mode_ofb_cfb(fake_kt.cipher));
         frame_finalize(&fake_frame, o->ce.link_mtu_defined, o->ce.link_mtu,
diff --git a/src/openvpn/ssl.c b/src/openvpn/ssl.c
index 315303b..747e176 100644
--- a/src/openvpn/ssl.c
+++ b/src/openvpn/ssl.c
@@ -1987,7 +1987,7 @@ tls_session_update_crypto_params(struct tls_session *session,
     }
 
     /* Update frame parameters: undo worst-case overhead, add actual overhead */
-    frame_add_to_extra_frame(frame, -(crypto_max_overhead()));
+    frame_remove_from_extra_frame(frame, (unsigned int) crypto_max_overhead());
     crypto_adjust_frame_parameters(frame, &session->opt->key_type,
                                    options->replay, packet_id_long_form);
     frame_finalize(frame, options->ce.link_mtu_defined, options->ce.link_mtu,