diff --git a/Modules/_blake2/impl/blake2b-ref.c b/Modules/_blake2/impl/blake2b-ref.c
index 7c1301bef68..ec775b4d4bb 100644
--- a/Modules/_blake2/impl/blake2b-ref.c
+++ b/Modules/_blake2/impl/blake2b-ref.c
@@ -307,8 +307,8 @@ int blake2b_update( blake2b_state *S, const uint8_t *in, uint64_t inlen )
     }
     else /* inlen <= fill */
     {
-      memcpy( S->buf + left, in, inlen );
-      S->buflen += inlen; /* Be lazy, do not compress */
+      memcpy( S->buf + left, in, (size_t)inlen );
+      S->buflen += (size_t)inlen; /* Be lazy, do not compress */
       in += inlen;
       inlen -= inlen;
     }
diff --git a/Modules/_blake2/impl/blake2s-ref.c b/Modules/_blake2/impl/blake2s-ref.c
index b90e8efc4ef..b08e72b7376 100644
--- a/Modules/_blake2/impl/blake2s-ref.c
+++ b/Modules/_blake2/impl/blake2s-ref.c
@@ -298,8 +298,8 @@ int blake2s_update( blake2s_state *S, const uint8_t *in, uint64_t inlen )
     }
     else /* inlen <= fill */
     {
-      memcpy( S->buf + left, in, inlen );
-      S->buflen += inlen; /* Be lazy, do not compress */
+      memcpy( S->buf + left, in, (size_t)inlen );
+      S->buflen += (size_t)inlen; /* Be lazy, do not compress */
       in += inlen;
       inlen -= inlen;
     }
diff --git a/setup.py b/setup.py
index ed1acfd847b..5450b7ed75b 100644
--- a/setup.py
+++ b/setup.py
@@ -894,7 +894,7 @@ def detect_modules(self):
         blake2_deps.append('hashlib.h')
 
         blake2_macros = []
-        if os.uname().machine == "x86_64":
+        if not cross_compiling and os.uname().machine == "x86_64":
             # Every x86_64 machine has at least SSE2.
             blake2_macros.append(('BLAKE2_USE_SSE', '1'))