diff --git a/lib/psci/psci_private.h b/lib/psci/psci_private.h
index e2dcfa8..72bd6bd 100644
--- a/lib/psci/psci_private.h
+++ b/lib/psci/psci_private.h
@@ -42,6 +42,11 @@
 			define_psci_cap(PSCI_SYSTEM_RESET2_AARCH64) |	\
 			define_psci_cap(PSCI_MEM_CHK_RANGE_AARCH64))
 
+/* Internally PSCI uses a uint16_t for various cpu indexes so
+ * define a limit to number of CPUs that can be initialised.
+ */
+#define PSCI_MAX_CPUS_INDEX	0xFFFFU
+
 /*
  * Helper functions to get/set the fields of PSCI per-cpu data.
  */
@@ -134,7 +139,7 @@
 	unsigned char level;
 
 	/* For indexing the psci_lock array*/
-	unsigned char lock_index;
+	uint16_t lock_index;
 } non_cpu_pd_node_t;
 
 typedef struct cpu_pwr_domain_node {
@@ -239,7 +244,7 @@
 #endif /* HW_ASSISTED_COHERENCY */
 
 static inline void psci_lock_init(non_cpu_pd_node_t *non_cpu_pd_node,
-				  unsigned char idx)
+				  uint16_t idx)
 {
 	non_cpu_pd_node[idx].lock_index = idx;
 }