diff --git a/roundcube-cleandb.sh b/roundcube-cleandb.sh
index 394824b..3c52a94 100755
--- a/roundcube-cleandb.sh
+++ b/roundcube-cleandb.sh
@@ -252,6 +252,21 @@ if [[ ! -x "$CLEANDB_SCRIPT" ]] ; then
    fatal "Script '${CLEANDB_SCRIPT}' is not executable!"
 fi
 
+# - 'cleandb.sh' starts with '#!/usr/bin/env php', so php must be found in
+#   the PATH of the executing user. Under cron the PATH usually lacks the
+#   php binary directory (e.g. /usr/local/php/bin) and contains directories
+#   like /root/bin, which are not accessible for $HTTP_USER ('env: php:
+#   Permission denied'). So determine php here and pass a clean PATH.
+# -
+PHP_BIN="$(command -v php 2> /dev/null)"
+if [[ -z "$PHP_BIN" ]] && [[ -x "/usr/local/php/bin/php" ]] ; then
+   PHP_BIN="/usr/local/php/bin/php"
+fi
+if [[ -z "$PHP_BIN" ]] ; then
+   fatal "No php binary found (neither in PATH nor '/usr/local/php/bin/php')!"
+fi
+RUN_PATH="$(dirname "$PHP_BIN"):/usr/local/bin:/usr/bin:/bin"
+
 
 if $terminal ; then
    echo ""
@@ -264,6 +279,7 @@ if $terminal ; then
    echo -e   "   Install directory (via htdocs).......: $INSTALL_DIR"
    echo -e   "   Script to be run......................: $CLEANDB_SCRIPT"
    echo -e   "   Executing user........................: $HTTP_USER"
+   echo -e   "   PHP binary............................: $PHP_BIN"
    echo ""
 fi
 
@@ -278,7 +294,8 @@ if $terminal ; then
 fi
 
 echononl "   Running 'cleandb.sh' for '${HOSTNAME_WEBMAIL}'.."
-su -c "$CLEANDB_SCRIPT" -s /bin/bash $HTTP_USER > $log_file 2>&1
+su -c "cd /tmp && export PATH=$(printf '%q' "$RUN_PATH") && $(printf '%q' "$CLEANDB_SCRIPT")" \
+   -s /bin/bash $HTTP_USER > $log_file 2>&1
 RC=$?
 
 if [[ $RC -eq 0 ]]; then