diff --git a/configure.ac b/configure.ac
index 1f2952e7..5bf81246 100644
--- a/configure.ac
+++ b/configure.ac
@@ -142,7 +142,7 @@ LIBS="$LIBS $BOOST_REGEX_LIBS"
 BOOST_THREAD
 AC_SUBST(BOOST_THREAD_LDFLAGS)
 AC_SUBST(BOOST_THREAD_LIBS)
-LDFLAGS+="$LDFLAGS $BOOST_THREAD_LDFLAGS"
+LDFLAGS="$LDFLAGS $BOOST_THREAD_LDFLAGS"
 LIBS="$LIBS $BOOST_THREAD_LIBS"
 
 # icu