diff --git a/configure.ac b/configure.ac
index ff41dc7267..5145c829d9 100644
--- a/configure.ac
+++ b/configure.ac
@@ -1055,6 +1055,7 @@ cat > conftest.cpp << EOF
 AUTOCONF_LOG4CPLUS_VERSION=LOG4CPLUS_VERSION_STR
 EOF
 
+# The tabulation below is NOT an error: PLEASE keep it.
 LOG4CPLUS_VERSION=`$CPPP $CPPFLAGS conftest.cpp | grep '^AUTOCONF_LOG4CPLUS_VERSION=' | $SED -e 's/^AUTOCONF_LOG4CPLUS_VERSION=//' -e 's/[[ 	]]//g' -e 's/"//g' 2> /dev/null`
 if test -z "$LOG4CPLUS_VERSION"; then
   LOG4CPLUS_VERSION="unknown"