diff --git a/include/bl31/sync_handle.h b/include/bl31/sync_handle.h
index 1ac4f98..ae61f31 100644
--- a/include/bl31/sync_handle.h
+++ b/include/bl31/sync_handle.h
@@ -55,6 +55,9 @@
  */
 int handle_sysreg_trap(uint64_t esr_el3, cpu_context_t *ctx);
 
+/* Handler for injecting UNDEF exception to lower EL */
+void inject_undef64(cpu_context_t *ctx);
+
 /* Prototypes for system register emulation handlers provided by platforms. */
 int plat_handle_impdef_trap(uint64_t esr_el3, cpu_context_t *ctx);
 int plat_handle_rng_trap(uint64_t esr_el3, cpu_context_t *ctx);