diff --git a/tool/m4/ruby_define_if.m4 b/tool/m4/ruby_define_if.m4
index 1cfd07b0c8..aba55783a2 100644
--- a/tool/m4/ruby_define_if.m4
+++ b/tool/m4/ruby_define_if.m4
@@ -1,12 +1,6 @@
 dnl -*- Autoconf -*-
 AC_DEFUN([RUBY_DEFINE_IF], [dnl
-    m4_ifval([$1], [AS_LITERAL_IF([$1], [], [test "X$1" = X || ])cat <<EOH >> confdefs.h
-@%:@if $1
-EOH
-])dnl
+    m4_ifval([$1], [AS_LITERAL_IF([$1], [], [test "X$1" = X || ])printf "@%:@if %s\n" "$1" >>confdefs.h])
 AC_DEFINE_UNQUOTED($2, $3)dnl
-    m4_ifval([$1], [AS_LITERAL_IF([$1], [], [test "X$1" = X || ])cat <<EOH >> confdefs.h
-@%:@endif /* $1 */
-EOH
-])dnl
+    m4_ifval([$1], [AS_LITERAL_IF([$1], [], [test "X$1" = X || ])printf "@%:@endif /* %s */\n" "$1" >>confdefs.h])
 ])dnl