diff --git a/configure.ac b/configure.ac
index 5b927d2b7ac1bd68f0ed6b3630937bf5a51502dd..6e4defefd2e8948e8acf6e5220c2ce66296676fa 100644
--- a/configure.ac
+++ b/configure.ac
@@ -37,7 +37,7 @@ AC_PROG_LIBTOOL
 AC_PROG_INSTALL
 
 dnl turn on warnings
-[CPPFLAGS="${CPPFLAGS} -Wall"]
+[CXXFLAGS="${CXXFLAGS} -Wall"]
 
 dnl Checks for options