diff --git a/library/threading.c b/library/threading.c
index 873b507..94404ac 100644
--- a/library/threading.c
+++ b/library/threading.c
@@ -148,6 +148,9 @@
 #if defined(THREADING_USE_GMTIME)
     mbedtls_mutex_init(&mbedtls_threading_gmtime_mutex);
 #endif
+#if defined(MBEDTLS_PSA_CRYPTO_C)
+    mbedtls_mutext_init(&mbedtls_threading_key_slot_mutex);
+#endif
 }
 
 /*
@@ -161,6 +164,9 @@
 #if defined(THREADING_USE_GMTIME)
     mbedtls_mutex_free(&mbedtls_threading_gmtime_mutex);
 #endif
+#if defined(MBEDTLS_PSA_CRYPTO_C)
+    mbedtls_mutex_free(&mbedtls_threading_key_slot_mutex);
+#endif
 }
 #endif /* MBEDTLS_THREADING_ALT */
 
@@ -176,5 +182,8 @@
 #if defined(THREADING_USE_GMTIME)
 mbedtls_threading_mutex_t mbedtls_threading_gmtime_mutex MUTEX_INIT;
 #endif
+#if defined(MBEDTLS_PSA_CRYPTO_C)
+mbedtls_threading_mutex_t mbedtls_threading_key_slot_mutex MUTEX_INIT;
+#endif
 
 #endif /* MBEDTLS_THREADING_C */