diff --git a/configure.ac b/configure.ac
index 285a2f9bcd..371cbf3da0 100644
--- a/configure.ac
+++ b/configure.ac
@@ -813,7 +813,7 @@ AS_IF([test "$GCC" = yes], [
 
     # disable fast-math
     for oflag in -fno-fast-math; do
-	RUBY_TRY_CFLAGS($oflag, [RUBY_APPEND_OPTION(CFLAGS, $oflag)])
+	RUBY_TRY_CFLAGS($oflag, [RUBY_APPEND_OPTION(optflags, $oflag)])
     done
     for oflag in -fexcess-precision=standard -fp-model\ precise; do
 	RUBY_TRY_CFLAGS($oflag, [RUBY_APPEND_OPTION(XCFLAGS, $oflag)])