diff --git a/configure.ac b/configure.ac
index ca35184c0..7d8648b2e 100644
--- a/configure.ac
+++ b/configure.ac
@@ -1142,20 +1142,6 @@ dnl
 dnl Header files
 dnl
 
-AC_DEFUN([RB_CHK_SYSHEADER],
-[
-	if test -z "$rb_have_sysheader_$2"; then
-		AC_CHECK_HEADER([$1],
-		[
-			rb_have_sysheader_$2=1;
-			AC_DEFINE([HAVE_$2], [1], [ Indication $1 is available. ])
-			RB_DEFINE_UNQUOTED([INC_$2], [$1>], [ The computed-include location of $1. ])
-		], [
-			RB_DEFINE_UNQUOTED([INC_$2], [stddef.h>], [ The dead-header in place of $1. ])
-		])
-	fi
-])
-
 AC_HEADER_STDBOOL
 dnl AC_HEADER_STDC
 
diff --git a/tools/m4/ratbox.m4 b/tools/m4/ratbox.m4
index 6a97128fc..792e68da1 100644
--- a/tools/m4/ratbox.m4
+++ b/tools/m4/ratbox.m4
@@ -51,3 +51,17 @@ AC_DEFUN([AM_COND_IF_NAND],
 		AM_COND_IF([$2], [], [$3])
 	])
 ])
+
+AC_DEFUN([RB_CHK_SYSHEADER],
+[
+	if test -z "$rb_cv_header_have_$2"; then
+		AC_CHECK_HEADER([$1],
+		[
+			rb_cv_header_have_$2=1;
+			AC_DEFINE([HAVE_$2], [1], [ Indication $1 is available. ])
+			RB_DEFINE_UNQUOTED([INC_$2], [$1>], [ The computed-include location of $1. ])
+		], [
+			RB_DEFINE_UNQUOTED([INC_$2], [stddef.h>], [ The dead-header in place of $1. ])
+		])
+	fi
+])