diff --git a/configure.in b/configure.in
index 4430da0e7..df1f41f64 100644
--- a/configure.in
+++ b/configure.in
@@ -95,7 +95,7 @@ dnl Compilation options
 dnl
 
 CFLAGS="$CFLAGS -ffast-math -fexpensive-optimizations"
-CXXFLAGS="$CFLAGS -ffast-math -fexpensive-optimizations"
+CXXFLAGS="$CXXFLAGS -ffast-math -fexpensive-optimizations"
 
 AC_MSG_CHECKING([whether to include debugging code])
 AC_ARG_ENABLE([debug],