diff --git a/library/psa_crypto.c b/library/psa_crypto.c
index a80f13d..98239c3 100644
--- a/library/psa_crypto.c
+++ b/library/psa_crypto.c
@@ -2735,7 +2735,7 @@
     status = psa_hash_update( &hmac->hash_ctx, ipad, block_size );
 
 cleanup:
-    mbedtls_platform_zeroize( ipad, key_length );
+    mbedtls_platform_zeroize( ipad, sizeof(ipad) );
 
     return( status );
 }