diff --git a/diskimage_builder/elements/ubuntu/pre-install.d/01-set-ubuntu-mirror b/diskimage_builder/elements/ubuntu/pre-install.d/01-set-ubuntu-mirror
index 71be18f95..efde2784d 100755
--- a/diskimage_builder/elements/ubuntu/pre-install.d/01-set-ubuntu-mirror
+++ b/diskimage_builder/elements/ubuntu/pre-install.d/01-set-ubuntu-mirror
@@ -12,7 +12,7 @@ DIB_DISTRIBUTION_MIRROR=${DIB_DISTRIBUTION_MIRROR:-}
 
 while IFS= read line
 do
-    if [[ "$line" =~ "${DIB_DISTRIBUTION_MIRROR_UBUNTU_IGNORE:-}" ]]; then
+    if [[ "$line" =~ ${DIB_DISTRIBUTION_MIRROR_UBUNTU_IGNORE:-} ]]; then
         # append line unmodified
         echo "$line" | tee --append /etc/apt/sources.list.new
     else