diff --git a/mozilla/security/manager/Makefile.in b/mozilla/security/manager/Makefile.in
index 47e050d6d80..1cb16272f49 100644
--- a/mozilla/security/manager/Makefile.in
+++ b/mozilla/security/manager/Makefile.in
@@ -177,6 +177,11 @@ DEFAULT_GMAKE_FLAGS += USE_DEBUG_RTL=1
 endif
 endif
 endif # WINNT
+ifeq ($(OS_ARCH),OS2)
+ifdef MOZ_OS2_HIGH_MEMORY
+DEFAULT_GMAKE_FLAGS += MOZ_OS2_HIGH_MEMORY=1
+endif
+endif # OS2
 # OS_CFLAGS needs to be passed on down.
 ifeq ($(OS_ARCH),OpenVMS)
 DEFAULT_GMAKE_FLAGS += XCFLAGS="$(OS_CFLAGS)"