diff --git a/xfce-test b/xfce-test
index 165b90a..d9a00c5 100755
--- a/xfce-test
+++ b/xfce-test
@@ -6,6 +6,7 @@ RUN_AS=
 LOG=${LOG:-/dev/stdout}
 PARALLEL_BUILDS=${PARALLEL_BUILDS:-0}
 TRAVIS=${TRAVIS:-FALSE}
+TAG=${TAG:-latest}
 
 is_my_git() {
   if git remote -v 2>/dev/null|grep "schuellerf/xfce-test" &>/dev/null; then
@@ -84,6 +85,38 @@ get-free-display(){
     done
 }
 
+# checks that the passed tag ($1) is available on Dockerhub or locally ($2)
+validate_tag(){
+    TAG="$1"
+
+    # check against whatever $2 is
+    case "$2" in
+        "Dockerhub")
+        tags="$(get_tags)"
+        location="on Dockerhub"
+    ;;
+        "local")
+        tags="$(get_local_tags)"
+        location="locally"
+    ;;
+    esac
+
+    for t in ${tags}; do
+        if [ "${t}" = "${TAG}" ]; then
+            return 0
+        fi
+    done
+
+    # the specified tag doesn't exist on Dockerhub or locally,
+    # so we list the available ones and return non-zero exit code
+    printf "The tag '%s' was not found %s\n" "${TAG}" "${location}"
+    printf -- "---\n"
+    printf "The following tags are available %s:\n" "${location}"
+    printf "%s\n" "${tags}"
+    return 1
+}
+
+
 # use this X display number for the tests
 export DISPLAY_NUM=$(get-free-display)
 
@@ -194,17 +227,6 @@ MODES_FOR_CASE=$(IFS=$'|'; echo "${WORK_MODES[*]}")
 shopt -s extglob
 MODES_FOR_CASE="+($MODES_FOR_CASE)"
 
-if [ -z $TAG ]; then
-  if is_my_git; then
-    TAG=$(git rev-parse --abbrev-ref HEAD 2>/dev/null|tr '/' '_')
-    if [[ $TAG == "last_tag" ]]; then
-        TAG=latest
-    fi
-  else
-    TAG=latest
-  fi
-fi
-
 if [ $# -ge 1 ]; then
     case $1 in
         "install")
@@ -227,7 +249,10 @@ if [ $# -ge 1 ]; then
         ;;
         "pull")
             if [ -n "$2" ]; then
-                TAG=$2
+                TAG="$2"
+                if ! validate_tag "${TAG}" "Dockerhub"; then
+                    exit 2
+                fi
             fi
 	    mode=$1
         ;;
@@ -439,6 +464,14 @@ case $mode in
     ;;
 esac
 
+# check whether the tag the user passed is actually valid
+if ! validate_tag "${TAG}" "Dockerhub" && \
+   ! ( printf "Attempting to find the tag '%s' locally...\n" "${TAG}" && \
+        validate_tag "${TAG}" "local" ); then
+    printf "Unable to find the tag '%s' either on Dockerhub or locally, exiting...\n" "${TAG}"
+    exit 1
+fi
+
 echo "You are working with the container: $TAG"
 
 # This starts the container for manual or semi automated tests