--- a/configure.in	Tue Dec 03 02:59:10 2002 +0200
+++ b/configure.in	Tue Dec 03 03:36:58 2002 +0200
@@ -333,6 +333,33 @@
 AC_DEFINE_UNQUOTED(OFF_T_MAX, $offt_max, Maximum value of off_t)
 AC_DEFINE_UNQUOTED(PRIuUOFF_T, "$uofft_fmt", printf() format for uoff_t)
 
+dnl * make sure size_t isn't signed. we'd probably work fine with it, but
+dnl * it's more likely vulnerable to buffer overflows. Anyway, C99 specifies
+dnl * that it's unsigned and only some old systems define it as signed.
+AC_MSG_CHECKING([whether size_t is signed])
+AC_TRY_RUN([
+  #include <sys/types.h>
+  int main() {
+    /* return 0 if we're signed */
+    exit((size_t)(int)-1 <= 0 ? 0 : 1);
+  }
+], [
+  AC_MSG_RESULT(yes)
+
+  echo
+  echo "Your system's size_t is a signed integer, Dovecot isn't designed to"
+  echo "support it. It probably works just fine, but it's less resistant to"
+  echo "buffer overflows. If you're not worried about this and still want to"
+  echo "compile Dovecot, set ignore_signed_size=1 environment."
+
+  if test "$ignore_signed_size" = ""; then
+    AC_ERROR([aborting])
+  fi
+  echo "..ignoring as requested.."
+], [
+  AC_MSG_RESULT(no)
+])
+
 AC_TYPEOF(ssize_t)
 case "$typeof_ssize_t" in
   long)