diff --git a/Makefile b/Makefile
index 1248997e834aeb5cc1c3323bf3f343b9ea5876c1..026932bf065902f06c36e5626110abc2d89ff1e3 100644
--- a/Makefile
+++ b/Makefile
@@ -26,6 +26,7 @@ SO_CFLAGS = -fPIC -D_SHARE=1
 SO_LDLAGS = -shared -fPIC
 endif
 
+ifndef SHARE
 DIFF ?= kvm
 ifneq ($(ISA),x86)
 ifeq ($(DIFF),kvm)
@@ -50,6 +51,7 @@ MKFLAGS = ISA=$(ISA) SHARE=1 ENGINE=interpreter
 else
 $(error invalid DIFF. Supported: qemu kvm nemu)
 endif
+endif
 
 OBJ_DIR ?= $(BUILD_DIR)/obj-$(ISA)-$(ENGINE)$(SO)
 BINARY ?= $(BUILD_DIR)/$(ISA)-$(NAME)-$(ENGINE)$(SO)