diff --git a/library/psa_crypto.c b/library/psa_crypto.c
index 5c9a828..c4f2209 100755
--- a/library/psa_crypto.c
+++ b/library/psa_crypto.c
@@ -1001,7 +1001,7 @@
                 if ( operation->ctx.hmac.hmac_ctx != NULL )
                 {
                     mbedtls_zeroize( operation->ctx.hmac.hmac_ctx, 
-                        sizeof(  operation->ctx.hmac.block_size * 2 ) );
+                                    operation->ctx.hmac.block_size * 2  );
                     mbedtls_free( operation->ctx.hmac.hmac_ctx );
                     operation->ctx.hmac.block_size = 0;
                 }