diff --git a/diskimage_builder/lib/common-functions b/diskimage_builder/lib/common-functions
index c33d4724..ac71350f 100644
--- a/diskimage_builder/lib/common-functions
+++ b/diskimage_builder/lib/common-functions
@@ -346,7 +346,7 @@ function unmount_dir {
 
     if [ ! -d $dir ]; then
         echo "*** $dir is not a directory"
-        return 1
+        return 0
     fi
 
     # get rid of any symlink elements in the incoming path, because
diff --git a/diskimage_builder/lib/img-functions b/diskimage_builder/lib/img-functions
index d1435438..d1163904 100644
--- a/diskimage_builder/lib/img-functions
+++ b/diskimage_builder/lib/img-functions
@@ -121,9 +121,7 @@ function finalise_base () {
         fi
     fi
     # Cleanup /tmp in the guest, so there is less cruft left there
-    if [ -d "$TMP_MOUNT_PATH/tmp" ]; then
-        unmount_dir $TMP_MOUNT_PATH/tmp
-    fi
+    unmount_dir $TMP_MOUNT_PATH/tmp
     find $TMP_MOUNT_PATH/tmp -maxdepth 1 -mindepth 1 | xargs sudo rm -rf --one-file-system
     # Truncate /var/log files in preparation for first boot
     sudo find ${TMP_MOUNT_PATH}/var/log -type f -exec cp /dev/null '{}' \;
diff --git a/tests/run_dib_library_tests.sh b/tests/run_dib_library_tests.sh
index a44408c4..c8f0549a 100755
--- a/tests/run_dib_library_tests.sh
+++ b/tests/run_dib_library_tests.sh
@@ -6,7 +6,7 @@
 # need a human in the loop.  Thus it's mostly useful for developers
 # during testing, but not so great for CI
 
-source ../lib/common-functions
+source ../diskimage_builder/lib/common-functions
 
 #
 # Directory mounting and unmounting
@@ -44,6 +44,14 @@ else
     echo "*** PASS all directories unmounted"
 fi
 
+# unmount missing dir
+if unmount_dir /this/path/does/not/exist/but/this/should/not/fail; then
+    echo "*** PASS unmount_dir ignored a missing path"
+else
+    echo "*** FAILED unmount_dir should ignore missing paths"
+    return 1
+fi
+
 # cleanup
 rm -rf $TMP_DIR