diff --git a/c_src/enacl_nif.c b/c_src/enacl_nif.c
index 78ca59e..bc31603 100644
--- a/c_src/enacl_nif.c
+++ b/c_src/enacl_nif.c
@@ -137,7 +137,7 @@ enif_crypto_curve25519_scalarmult(ErlNifEnv *env, int argc,
   memcpy(bp, basepoint.data, crypto_scalarmult_curve25519_BYTES);
 
   /* Clear the high-bit. Better safe than sorry. */
-  bp[31] &= 0x7f;
+  bp[crypto_scalarmult_curve25519_BYTES - 1] &= 0x7f;
 
   do {
     if (!enif_alloc_binary(crypto_scalarmult_curve25519_BYTES, &output)) {
@@ -1174,7 +1174,6 @@ static void uint64_pack(unsigned char *y, ErlNifUInt64 x) {
   *y++ = x;
   x >>= 8;
   *y++ = x;
-  x >>= 8;
 }
 
 static ErlNifUInt64 uint64_unpack(const unsigned char *x) {
diff --git a/eqc_test/enacl_eqc.erl b/eqc_test/enacl_eqc.erl
index e2978dc..b0f4859 100644
--- a/eqc_test/enacl_eqc.erl
+++ b/eqc_test/enacl_eqc.erl
@@ -1,6 +1,6 @@
 -module(enacl_eqc).
 -include_lib("eqc/include/eqc.hrl").
--compile(export_all).
+-compile([export_all, nowarn_export_all]).
 
 -ifndef(mini).
 -compile({parse_transform, eqc_parallelize}).
@@ -828,8 +828,26 @@ prop_randombytes() ->
                 end
        end).
 
+%% SCRAMBLING
+prop_scramble_block() ->
+    ?FORALL({Block, Key}, {binary(16), eqc_gen:largebinary(32)},
+        is_binary(enacl_ext:scramble_block_16(Block, Key))).
+
+%% Scala multiplication
+prop_scalarmult() ->
+  Bytes = 32,
+  ?FORALL({S1, S2, Basepoint}, {binary(Bytes), binary(Bytes), binary(Bytes)},
+          equals(enacl:curve25519_scalarmult(S1,
+                       enacl:curve25519_scalarmult(S2, Basepoint)),
+                 enacl:curve25519_scalarmult(S2,
+                       enacl:curve25519_scalarmult(S1, Basepoint)))
+         ).
+
+%% HELPERS
+
 %% INTERNAL FUNCTIONS
 %% ------------------------------------------------------------
+
 badargs(Thunk) ->
   try
     Thunk(),