diff --git a/configure.ac b/configure.ac
index ca184f22f..69c0d93fb 100644
--- a/configure.ac
+++ b/configure.ac
@@ -616,13 +616,16 @@ dnl
 
 AC_DEFUN([RB_CHK_SYSHEADER],
 [
-	AC_CHECK_HEADER([$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 $1. ])
-	])
+	if test -z "$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