diff --git a/configure.ac b/configure.ac
index 6c8311dbe8..6cea43d0c9 100644
--- a/configure.ac
+++ b/configure.ac
@@ -579,7 +579,7 @@ AS_IF([test "$GCC" = yes], [
 		  AS_HELP_STRING([--disable-fortify-source],
 				 [disable -D_FORTIFY_SOURCE=2 option, which causes link error on mingw]),
 		  [fortify_source=$enableval])
-    AS_IF([test "x$fortify_source" = xno], [
+    AS_IF([test "x$fortify_source" != xno], [
     RUBY_TRY_CFLAGS(-D_FORTIFY_SOURCE=2, [RUBY_APPEND_OPTION(XCFLAGS, -D_FORTIFY_SOURCE=2)])
     ])