diff --git a/library/psa_crypto_slot_management.c b/library/psa_crypto_slot_management.c
index 2d24e6d..180aecb 100644
--- a/library/psa_crypto_slot_management.c
+++ b/library/psa_crypto_slot_management.c
@@ -147,7 +147,14 @@
 
 psa_status_t psa_initialize_key_slots(void)
 {
-    /* Nothing to do: program startup and psa_wipe_all_key_slots() both
+#if defined(MBEDTLS_THREADING_C)
+    /* Initialize the global key slot mutex. */
+    if (!global_data.key_slots_initialized) {
+        mbedtls_mutex_init(&global_data.key_slot_mutex);
+    }
+#endif
+
+    /* Program startup and psa_wipe_all_key_slots() both
      * guarantee that the key slots are initialized to all-zero, which
      * means that all the key slots are in a valid, empty state. */
     global_data.key_slots_initialized = 1;
@@ -164,6 +171,14 @@
         slot->state = PSA_SLOT_PENDING_DELETION;
         (void) psa_wipe_key_slot(slot);
     }
+
+#if defined(MBEDTLS_THREADING_C)
+    /* Free the global key slot mutex. */
+    if (global_data.key_slots_initialized) {
+        mbedtls_mutex_free(&global_data.key_slot_mutex);
+    }
+#endif
+
     global_data.key_slots_initialized = 0;
 }
 
diff --git a/library/psa_crypto_slot_management.h b/library/psa_crypto_slot_management.h
index 0b0d7b3..01778f8 100644
--- a/library/psa_crypto_slot_management.h
+++ b/library/psa_crypto_slot_management.h
@@ -85,6 +85,10 @@
                                        psa_key_slot_t **p_slot);
 
 /** Initialize the key slot structures.
+ * If multi-threading is enabled then initialize the key slot mutex.
+ * This function is not thread-safe,
+ * if called by competing threads the key slot mutex may be initialized
+ * more than once.
  *
  * \retval #PSA_SUCCESS
  *         Currently this function always succeeds.
@@ -92,6 +96,10 @@
 psa_status_t psa_initialize_key_slots(void);
 
 /** Delete all data from key slots in memory.
+ * If multi-threading is enabled then free the key slot mutex.
+ * This function is not thread-safe,
+ * if called by competing threads the key slot mutex may be freed
+ * more than once.
  *
  * This does not affect persistent storage. */
 void psa_wipe_all_key_slots(void);