diff --git a/extras/vpnupgrade.sh b/extras/vpnupgrade.sh
index 1a4616d..88f0d0e 100644
--- a/extras/vpnupgrade.sh
+++ b/extras/vpnupgrade.sh
@@ -161,6 +161,7 @@ fi
 /bin/rm -rf "/opt/src/libreswan-$SWAN_VER"
 tar xzf "$swan_file" && /bin/rm -f "$swan_file"
 cd "libreswan-$SWAN_VER" || exiterr "Cannot enter Libreswan source dir."
+sed -i '/^#define LSWBUF_CANARY/s/-2$/((char) -2)/' include/lswlog.h
 cat > Makefile.inc.local <<'EOF'
 WERROR_CFLAGS =
 USE_DNSSEC = false
diff --git a/extras/vpnupgrade_centos.sh b/extras/vpnupgrade_centos.sh
index f7337ff..ee2ad84 100644
--- a/extras/vpnupgrade_centos.sh
+++ b/extras/vpnupgrade_centos.sh
@@ -139,6 +139,7 @@ fi
 /bin/rm -rf "/opt/src/libreswan-$SWAN_VER"
 tar xzf "$swan_file" && /bin/rm -f "$swan_file"
 cd "libreswan-$SWAN_VER" || exiterr "Cannot enter Libreswan source dir."
+sed -i '/^#define LSWBUF_CANARY/s/-2$/((char) -2)/' include/lswlog.h
 cat > Makefile.inc.local <<'EOF'
 WERROR_CFLAGS =
 USE_DNSSEC = false
diff --git a/vpnsetup.sh b/vpnsetup.sh
index a4eedb8..30cd001 100755
--- a/vpnsetup.sh
+++ b/vpnsetup.sh
@@ -191,6 +191,7 @@ fi
 /bin/rm -rf "/opt/src/libreswan-$SWAN_VER"
 tar xzf "$swan_file" && /bin/rm -f "$swan_file"
 cd "libreswan-$SWAN_VER" || exiterr "Cannot enter Libreswan source dir."
+sed -i '/^#define LSWBUF_CANARY/s/-2$/((char) -2)/' include/lswlog.h
 cat > Makefile.inc.local <<'EOF'
 WERROR_CFLAGS =
 USE_DNSSEC = false
diff --git a/vpnsetup_centos.sh b/vpnsetup_centos.sh
index 8cb8401..8c6513b 100755
--- a/vpnsetup_centos.sh
+++ b/vpnsetup_centos.sh
@@ -175,6 +175,7 @@ fi
 /bin/rm -rf "/opt/src/libreswan-$SWAN_VER"
 tar xzf "$swan_file" && /bin/rm -f "$swan_file"
 cd "libreswan-$SWAN_VER" || exiterr "Cannot enter Libreswan source dir."
+sed -i '/^#define LSWBUF_CANARY/s/-2$/((char) -2)/' include/lswlog.h
 cat > Makefile.inc.local <<'EOF'
 WERROR_CFLAGS =
 USE_DNSSEC = false