diff --git a/gconfig/UNIX.mk b/gconfig/UNIX.mk
index 4b07cab0c59..5859cffdb63 100644
--- a/gconfig/UNIX.mk
+++ b/gconfig/UNIX.mk
@@ -53,6 +53,7 @@ NATIVE_JULIAN_DLL=julian
 PLATFORM_DIRECTORY=unix
 NATIVE_ZLIB_DLL=zlib
 NATIVE_XP_DLL=xp
+XP_PREF_DLL=pref
 AR_ALL =
 AR_NONE =
 
diff --git a/gconfig/WIN32.mk b/gconfig/WIN32.mk
index 031946ea91f..91635702e06 100644
--- a/gconfig/WIN32.mk
+++ b/gconfig/WIN32.mk
@@ -56,6 +56,7 @@ NATIVE_JULIAN_DLL=juls$(MOZ_BITS)$(VERSION_NUMBER)
 PLATFORM_DIRECTORY=windows
 NATIVE_ZLIB_DLL=zip$(MOZ_BITS)$(VERSION_NUMBER)
 NATIVE_XP_DLL=xplib
+XP_PREF_DLL=xppref$(MOZ_BITS)
 
 ifdef RCFILE
 RCFILE       := $(RCFILE).rc