diff --git a/build.sh b/build.sh
index ddf4b07..dfa35af 100755
--- a/build.sh
+++ b/build.sh
@@ -93,8 +93,7 @@ then
     echo "Start building supported kopano $component image version ($currentVersion)..."
     set -x
     # build it
-    if docker build \
-                 --pull \
+    if docker build --pull \
                  --build-arg "KOPANO_${component^^}_REPOSITORY_URL=https://serial:$serial@download.kopano.io/supported/$component:/$branch/Debian_9.0" \
                  --build-arg RELEASE_KEY_DOWNLOAD=1 \
                  --build-arg "DOWNLOAD_COMMUNITY_PACKAGES=0" \
diff --git a/core/Dockerfile b/core/Dockerfile
index 471834e..bf641fe 100644
--- a/core/Dockerfile
+++ b/core/Dockerfile
@@ -50,7 +50,7 @@ RUN \
     fi; \
     echo "deb [${KOPANO_REPOSITORY_FLAGS}] ${KOPANO_CORE_REPOSITORY_URL} ./" > /etc/apt/sources.list.d/kopano.list; \
     # save kopano version if supported kopano
-    if [ -z /kopano/buildversion ]; then \
+    if [ ! -f /kopano/buildversion ]; then \
         echo "core-${KOPANO_CORE_VERSION}" > /kopano/buildversion; \
     fi; \
     # install apt key if supported kopano
diff --git a/webapp/Dockerfile b/webapp/Dockerfile
index b9ca21f..c919fd0 100644
--- a/webapp/Dockerfile
+++ b/webapp/Dockerfile
@@ -51,7 +51,7 @@ RUN \
     echo "deb [${KOPANO_REPOSITORY_FLAGS}] ${KOPANO_CORE_REPOSITORY_URL} ./" > /etc/apt/sources.list.d/kopano.list; \
     echo "deb [${KOPANO_REPOSITORY_FLAGS}] ${KOPANO_WEBAPP_REPOSITORY_URL} ./" >> /etc/apt/sources.list.d/kopano.list; \
     # save kopano version if supported kopano
-    if [ -z /kopano/buildversion ]; then \
+    if [ ! -f /kopano/buildversion ]; then \
         echo "core-${KOPANO_CORE_VERSION}" > /kopano/buildversion; \
         echo "webapp-${KOPANO_WEBAPP_VERSION}" >> /kopano/buildversion; \
     fi; \