diff --git a/target/i386/helper.c b/target/i386/helper.c
index e0aaed3c4c..651041ccfa 100644
--- a/target/i386/helper.c
+++ b/target/i386/helper.c
@@ -110,6 +110,7 @@ int cpu_x86_support_mca_broadcast(CPUX86State *env)
 /* x86 mmu */
 /* XXX: add PGE support */
 
+#ifndef CONFIG_USER_ONLY
 void x86_cpu_set_a20(X86CPU *cpu, int a20_state)
 {
     CPUX86State *env = &cpu->env;
@@ -129,6 +130,7 @@ void x86_cpu_set_a20(X86CPU *cpu, int a20_state)
         env->a20_mask = ~(1 << 20) | (a20_state << 20);
     }
 }
+#endif
 
 void cpu_x86_update_cr0(CPUX86State *env, uint32_t new_cr0)
 {