diff --git a/configure.ac b/configure.ac
index d1e2f4520..b90a234bc 100644
--- a/configure.ac
+++ b/configure.ac
@@ -210,7 +210,7 @@ if test "x$ac_cv_lib_pthread_pthread_exit" != "xyes" \
     dnl fails.  See if we need -pthread instead of -lpthread and look
     dnl for the functions in libc_r.
     save_CXXFLAGS="$CXXFLAGS"
-    save_CFLAGS="$FLAGS"
+    save_CFLAGS="$CFLAGS"
     CXXFLAGS="-pthread $CXXFLAGS"
     CFLAGS="-pthread $FLAGS"
     save_LIBS=$LIBS