diff --git a/mozilla/security/coreconf/OS2.mk b/mozilla/security/coreconf/OS2.mk
index 6b43b22c127..e9d0c69006a 100644
--- a/mozilla/security/coreconf/OS2.mk
+++ b/mozilla/security/coreconf/OS2.mk
@@ -227,6 +227,8 @@ else
 	endif
 endif
 
+DEFINES += -DXP_OS2
+
 define MAKE_OBJDIR
 if test ! -d $(@D); then rm -rf $(@D); $(NSINSTALL) -D $(@D); fi
 endef