diff --git a/ChangeLog b/ChangeLog
index 722f55c3b..efbc7a786 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,13 @@
+2009-09-16  Robert Millan  <rmh.grub@aybabtu.com>
+
+	* aclocal.m4 (AC_LANG_PROGRAM): New macro.  Overrides stock
+	AC_LANG_PROGRAM from autoconf.
+	(grub_ASM_USCORE, grub_PROG_OBJCOPY_ABSOLUTE): Add missing
+	prototypes (fixes warning).
+
+	* configure.ac: Add `-Werror' to TARGET_CFLAGS unless
+	`--disable-werror' was used.
+
 2009-09-16  Robert Millan  <rmh.grub@aybabtu.com>
 
 	* partmap/msdos.c (pc_partition_map_iterate): Fix possible use of
diff --git a/aclocal.m4 b/aclocal.m4
index 313b241fa..899eca409 100644
--- a/aclocal.m4
+++ b/aclocal.m4
@@ -1,3 +1,18 @@
+dnl Redefine AC_LANG_PROGRAM with a "-Wstrict-prototypes -Werror"-friendly
+dnl version.  Patch submitted to bug-autoconf in 2009-09-16.
+m4_define([AC_LANG_PROGRAM(C)],
+[$1
+int
+main (void)
+{
+dnl Do *not* indent the following line: there may be CPP directives.
+dnl Don't move the `;' right after for the same reason.
+$2
+  ;
+  return 0;
+}])
+
+
 dnl Check whether target compiler is working
 AC_DEFUN(grub_PROG_TARGET_CC,
 [AC_MSG_CHECKING([whether target compiler is working])
@@ -26,6 +41,7 @@ AC_DEFUN(grub_ASM_USCORE,
 AC_MSG_CHECKING([if C symbols get an underscore after compilation])
 AC_CACHE_VAL(grub_cv_asm_uscore,
 [cat > conftest.c <<\EOF
+int func (int *);
 int
 func (int *list)
 {
@@ -63,6 +79,7 @@ AC_DEFUN(grub_PROG_OBJCOPY_ABSOLUTE,
 [AC_MSG_CHECKING([whether ${OBJCOPY} works for absolute addresses])
 AC_CACHE_VAL(grub_cv_prog_objcopy_absolute,
 [cat > conftest.c <<\EOF
+void cmain (void);
 void
 cmain (void)
 {
diff --git a/configure.ac b/configure.ac
index 37ecba759..59e8510d3 100644
--- a/configure.ac
+++ b/configure.ac
@@ -390,6 +390,13 @@ if test x"$sap_possible" = xyes; then
   TARGET_CFLAGS="$TARGET_CFLAGS -mno-stack-arg-probe"
 fi
 
+AC_ARG_ENABLE([werror],
+	      [AS_HELP_STRING([--disable-werror],
+                             [do not use -Werror when building GRUB])])
+if test x"$enable_werror" != xno ; then
+  TARGET_CFLAGS="$TARGET_CFLAGS -Werror"
+fi
+
 AC_SUBST(TARGET_CFLAGS)
 AC_SUBST(TARGET_MODULE_FORMAT)
 AC_SUBST(OBJCONV)