diff --git a/diskimage_builder/elements/bootloader/cleanup.d/51-bootloader b/diskimage_builder/elements/bootloader/cleanup.d/51-bootloader
index 1ba0485e..28e02b6a 100755
--- a/diskimage_builder/elements/bootloader/cleanup.d/51-bootloader
+++ b/diskimage_builder/elements/bootloader/cleanup.d/51-bootloader
@@ -39,7 +39,7 @@ fi
 select_boot_kernel_initrd $TARGET_ROOT
 
 # Serial console on Power is hvc0
-if [ "powerpc ppc64 ppc64le" =~ "$ARCH" ] ; then
+if [[ "powerpc ppc64 ppc64le" =~ "$ARCH" ]] ; then
     SERIAL_CONSOLE="hvc0"
 else
     SERIAL_CONSOLE="ttyS0,115200"
diff --git a/diskimage_builder/elements/bootloader/finalise.d/50-bootloader b/diskimage_builder/elements/bootloader/finalise.d/50-bootloader
index 162e4ab0..4b9f9df7 100755
--- a/diskimage_builder/elements/bootloader/finalise.d/50-bootloader
+++ b/diskimage_builder/elements/bootloader/finalise.d/50-bootloader
@@ -147,7 +147,7 @@ function install_grub2 {
     echo 'GRUB_GFXPAYLOAD_LINUX=text' >>/etc/default/grub
 
     # Serial console on Power is hvc0
-    if [ "powerpc ppc64 ppc64le" =~ "$ARCH" ] ; then
+    if [[ "powerpc ppc64 ppc64le" =~ "$ARCH" ]]; then
         SERIAL_CONSOLE="hvc0"
     else
         SERIAL_CONSOLE="ttyS0,115200"