diff --git a/compiletime-settings.devel b/compiletime-settings.devel
index 76f69ce0bf..daf96eac1c 100644
--- a/compiletime-settings.devel
+++ b/compiletime-settings.devel
@@ -1,6 +1,7 @@
 config {
   experimental on
   debug on
+  ubsan on
   system-wa off
   sysconfdir /etc
   fdtarball dosemu-freedos-1.0-bin.tgz
diff --git a/default-configure b/default-configure
index 28702c9454..aade60eea0 100755
--- a/default-configure
+++ b/default-configure
@@ -53,6 +53,9 @@ while [ "$1" != "" ]; do
     asan)
       if [ "$2" = "on" ]; then STRING="$STRING --enable-asan"; fi
       ;;
+    ubsan)
+      if [ "$2" = "on" ]; then STRING="$STRING --enable-ubsan"; fi
+      ;;
     system-wa)
       if [ "$2" = "off" ]; then STRING="$STRING --disable-system-wa"; fi
       ;;