diff --git a/Makefile b/Makefile
index fbd7d8a..99b1723 100644
--- a/Makefile
+++ b/Makefile
@@ -17,8 +17,9 @@ TEMPLATE_ENV_WHITELIST += \
 	DIST DISTRIBUTION TEMPLATE_SCRIPTS TEMPLATE_NAME TEMPLATE_FLAVOR \
 	TEMPLATE_FLAVOR_DIR TEMPLATE_OPTIONS APPMENUS_DIR \
 	VERBOSE DEBUG PATH BUILDER_DIR SRC_DIR DISCARD_PREPARED_IMAGE \
-	TEMPLATE_ROOT_WITH_PARTITIONS USE_QUBES_REPO_VERSION \
-	USE_QUBES_REPO_TESTING BUILDER_TURBO_MODE REPO_PROXY FEDORA_MIRROR \
+	TEMPLATE_ROOT_WITH_PARTITIONS TEMPLATE_ROOT_SIZE \
+	USE_QUBES_REPO_VERSION USE_QUBES_REPO_TESTING \
+	BUILDER_TURBO_MODE REPO_PROXY FEDORA_MIRROR \
 	CENTOS_MIRROR EPEL_MIRROR
 
 # Make sure names are < 32 characters, process aliases
diff --git a/prepare_image b/prepare_image
index 69d2582..7a667fd 100755
--- a/prepare_image
+++ b/prepare_image
@@ -28,6 +28,10 @@ if [ "${VERBOSE}" == "1" ]; then
     export YUM_OPTS="${YUM_OPTS} -q"
 fi
 
+if [ -z "$TEMPLATE_ROOT_SIZE" ]; then
+    TEMPLATE_ROOT_SIZE=10G
+fi
+
 # ------------------------------------------------------------------------------
 # Make sure INSTALLDIR exists
 # ------------------------------------------------------------------------------
@@ -54,7 +58,7 @@ if [ -f "${IMG}" ]; then
     fi
 else
     echo "-> Initializing empty image..."
-    truncate -s 10G "${IMG}" || exit 1
+    truncate -s "$TEMPLATE_ROOT_SIZE" "${IMG}" || exit 1
 
     if [ "0$TEMPLATE_ROOT_WITH_PARTITIONS" -eq 1 ]; then
         echo "-> Creating partition table"