diff --git a/compat-usrmerge.changes b/compat-usrmerge.changes
index eb5757f..f7108d0 100644
--- a/compat-usrmerge.changes
+++ b/compat-usrmerge.changes
@@ -1,3 +1,9 @@
+-------------------------------------------------------------------
+Wed Jun  2 15:29:15 UTC 2021 - Ludwig Nussel <lnussel@suse.com>
+
+- exit early if one of the affected directories has mountpoint
+  beneath it
+
 -------------------------------------------------------------------
 Tue Jun  1 23:27:08 UTC 2021 - Niklas Haas <obs@haasn.xyz>
 
diff --git a/convertfs b/convertfs
index b2a8c27..2a2a2fc 100644
--- a/convertfs
+++ b/convertfs
@@ -25,6 +25,15 @@ mountpoint -q "$ROOT/usr" || CP_HARDLINK="-l"
 
 set -e
 
+while read dev mp other; do
+    for dir in bin sbin lib lib64; do
+	if [ "${mp#$ROOT/$dir}" != "$mp" ] || [ "${mp#$ROOT/usr/$dir}" != "$mp" ]; then
+	    echo "Please unmount $mp before the conversion"
+	    exit 1
+	fi
+    done
+done < /proc/mounts
+
 # merge / and /usr in new dir in /usr
 for dir in bin sbin lib lib64; do
     rm -rf -- "$ROOT/usr/${dir}.usrmerge"
@@ -43,7 +52,7 @@ for dir in bin sbin lib lib64; do
 	    rm -rf "$f.usrmerge~"
 	    mv "$f" "$f.usrmerge~"
 	fi
-    done < <(find "$ROOT/usr/$dir" -type d -printf "%P\n" )
+    done < <(find "$ROOT/usr/$dir" -xdev -type d -printf "%P\n" )
     echo "Merge the copy with \`$ROOT/usr/$dir'."
     [[ -d "$ROOT/usr/${dir}.usrmerge" ]] \
         || mkdir -p "$ROOT/usr/${dir}.usrmerge"
@@ -51,14 +60,14 @@ for dir in bin sbin lib lib64; do
     echo "Clean up duplicates in \`$ROOT/usr/$dir'."
     # delete all symlinks that have been backed up. /usr versions
     # override / ones
-    find "$ROOT/usr/${dir}.usrmerge" -type l -name '*.usrmerge~' -delete || :
+    find "$ROOT/usr/${dir}.usrmerge" -xdev -type l -name '*.usrmerge~' -delete || :
     # in rare cases the symlinks may point from /usr to /, so remove
     # the link in that case
     while read file; do
 	o=${file%%.usrmerge~}
 	[ -L "$o" ] && mv -f "$file" "$o"
     done < <(find "$ROOT/usr/${dir}.usrmerge" \
-        -name '*.usrmerge~' -type f)
+        -xdev -name '*.usrmerge~' -type f)
 done
 # switch over merged dirs in /usr
 for dir in bin sbin lib lib64; do
@@ -72,7 +81,7 @@ done
 for dir in bin sbin lib lib64; do
     if [ ! -L "$ROOT/$dir" -a -d "$ROOT/$dir" ]; then
 	  echo "Create \`$ROOT/$dir' symlink."
-	  rm -rf "$ROOT/${dir}.usrmerge" || :
+	  rm --one-file-system -rf "$ROOT/${dir}.usrmerge" || :
 	  ln -s usr/$dir "$ROOT/${dir}.usrmerge"
 	  /usr/libexec/xmv "$ROOT/$dir" "$ROOT/${dir}.usrmerge"
     fi
@@ -88,7 +97,7 @@ for dir in bin sbin lib lib64; do
 	if [ -d "$d" ]; then
 	    echo "$d ..."
 	    mv "$d" "$d~"
-	    rm -rf "$d~"
+	    rm --one-file-system -rf "$d~"
 	fi
     done
 done