diff --git a/library/psa_crypto.c b/library/psa_crypto.c
index 7d78827453..4b17e5594f 100644
--- a/library/psa_crypto.c
+++ b/library/psa_crypto.c
@@ -2941,7 +2941,7 @@ psa_status_t psa_generate_key( psa_key_slot_t key,
 
 void mbedtls_psa_crypto_free( void )
 {
-    size_t key;
+    psa_key_slot_t key;
     for( key = 1; key < PSA_KEY_SLOT_COUNT; key++ )
         psa_destroy_key( key );
     mbedtls_ctr_drbg_free( &global_data.ctr_drbg );