diff --git a/mozilla/xpcom/typelib/xpt/src/Makefile.in b/mozilla/xpcom/typelib/xpt/src/Makefile.in
index 2bcea10de47..779de215028 100644
--- a/mozilla/xpcom/typelib/xpt/src/Makefile.in
+++ b/mozilla/xpcom/typelib/xpt/src/Makefile.in
@@ -52,8 +52,12 @@ libhostxpt.$(LIB_SUFFIX): $(HOSTOBJS)
 	$(AR) $(AR_FLAGS) $@ $(HOSTOBJS)
 	$(RANLIB) $@
 
+ifdef HOST_NSPR_MDCPUCFG
+HOST_CFLAGS     += -DMDCPUCFG=$(HOST_NSPR_MDCPUCFG)
+endif
+
 %.o-h: %.c
-	$(HOST_CC) $(HOST_CFLAGS) -I$(DIST)/include $(NSPR_CFLAGS) -DMDCPUCFG=$(HOST_NSPR_MDCPUCFG) -c -o $@ $<
+	$(HOST_CC) $(HOST_CFLAGS) -I$(DIST)/include $(NSPR_CFLAGS) -c -o $@ $<
 
 export:: libhostxpt.$(LIB_SUFFIX)
 	$(INSTALL) -m 444 libhostxpt.$(LIB_SUFFIX) $(DIST)/lib