diff --git a/extmod/modtrezorcrypto/modtrezorcrypto-pbkdf2.h b/extmod/modtrezorcrypto/modtrezorcrypto-pbkdf2.h
index d9525b736..fbf383b71 100644
--- a/extmod/modtrezorcrypto/modtrezorcrypto-pbkdf2.h
+++ b/extmod/modtrezorcrypto/modtrezorcrypto-pbkdf2.h
@@ -87,12 +87,18 @@ STATIC mp_obj_t mod_TrezorCrypto_Pbkdf2_key(mp_obj_t self) {
     mp_obj_Pbkdf2_t *o = MP_OBJ_TO_PTR(self);
     vstr_t vstr;
     if (o->prf == 256) {
+        PBKDF2_HMAC_SHA256_CTX ctx;
+        memcpy(&ctx, &(o->ctx256), sizeof(PBKDF2_HMAC_SHA256_CTX));
         vstr_init_len(&vstr, SHA256_DIGEST_LENGTH);
-        memcpy(vstr.buf, o->ctx256.f, SHA256_DIGEST_LENGTH);
+        pbkdf2_hmac_sha256_Final(&ctx, (uint8_t *)vstr.buf);
+        memset(&ctx, 0, sizeof(PBKDF2_HMAC_SHA256_CTX));
     }
     if (o->prf == 512) {
+        PBKDF2_HMAC_SHA512_CTX ctx;
+        memcpy(&ctx, &(o->ctx512), sizeof(PBKDF2_HMAC_SHA512_CTX));
         vstr_init_len(&vstr, SHA512_DIGEST_LENGTH);
-        memcpy(vstr.buf, o->ctx512.f, SHA512_DIGEST_LENGTH);
+        pbkdf2_hmac_sha512_Final(&ctx, (uint8_t *)vstr.buf);
+        memset(&ctx, 0, sizeof(PBKDF2_HMAC_SHA512_CTX));
     }
     return mp_obj_new_str_from_vstr(&mp_type_bytes, &vstr);
 }