diff --git a/include/functions b/include/functions
index 95083600..e8965986 100644
--- a/include/functions
+++ b/include/functions
@@ -1717,7 +1717,7 @@
         if [ ! -z "${RPMBINARY}" ]; then
             output=$(${RPMBINARY} --quiet -q ${package} 2> /dev/null)
             exit_code=$?
-        elif ! -z "${DPKGBINARY}" ]; then
+        elif [ ! -z "${DPKGBINARY}" ]; then
             output=$(${DPKGBINARY} -l ${package} 2> /dev/null)
             exit_code=$?
         elif [ ! -z "${ZYPPERBINARY}" ]; then