diff --git a/tool/m4/ruby_default_arch.m4 b/tool/m4/ruby_default_arch.m4
index a53bb5fc41..a9e7177fda 100644
--- a/tool/m4/ruby_default_arch.m4
+++ b/tool/m4/ruby_default_arch.m4
@@ -2,6 +2,7 @@
 AC_DEFUN([RUBY_DEFAULT_ARCH], [
 AC_MSG_CHECKING([arch option])
 AS_CASE([$1],
+	[arm64],      [],
 	[*64],        [ARCH_FLAG=-m64],
 	[[i[3-6]86]], [ARCH_FLAG=-m32],
 	[AC_MSG_ERROR(unknown target architecture: $target_archs)]
diff --git a/tool/m4/ruby_universal_arch.m4 b/tool/m4/ruby_universal_arch.m4
index dd9ad7ee46..e2f698cbc0 100644
--- a/tool/m4/ruby_universal_arch.m4
+++ b/tool/m4/ruby_universal_arch.m4
@@ -39,7 +39,7 @@ AS_IF([test ${target_archs+set}], [
 	    echo 'int main(){return 0;}' > conftest.c
 	    AS_IF([$CC $CFLAGS $ARCH_FLAG -o conftest conftest.c > /dev/null 2>&1], [
 		rm -fr conftest.*
-	    ], [
+	    ], [test -z "$ARCH_FLAG"], [
 		RUBY_DEFAULT_ARCH("$target_archs")
 	    ])
 	])