diff --git a/configure.ac b/configure.ac
index 03e05847..82af3a20 100644
--- a/configure.ac
+++ b/configure.ac
@@ -5,7 +5,7 @@ AC_PREREQ(2.50)
 
 AC_CONFIG_HEADERS([irssi-config.h])
 AC_CONFIG_MACRO_DIR([m4])
-AM_INIT_AUTOMAKE([1.9 no-define foreign])
+AM_INIT_AUTOMAKE([1.9 no-define foreign subdir-objects])
 
 AM_SILENT_RULES([yes])
 
@@ -199,6 +199,12 @@ case "$host_os" in
   hpux*)
     CFLAGS="$CFLAGS -D_XOPEN_SOURCE_EXTENDED"
     ;;
+  os400*)
+    dnl IBM i uses ppc64 gcc by default, but binutils defaults to 32-bit. Force
+    dnl IBM binutils, and force it into ppc64 mode. This isn't set for AIX
+    dnl because gcc there defaults to ppc32.
+    AR="/usr/bin/ar -X64"
+    ;;
   *)
     ;;
 esac