diff --git a/ext/digest/sha1/sha1.c b/ext/digest/sha1/sha1.c
index ce20027..d9bd30b 100644
--- a/ext/digest/sha1/sha1.c
+++ b/ext/digest/sha1/sha1.c
@@ -220,14 +220,15 @@ int SHA1_Init(SHA1_CTX *context)
  */
 void SHA1_Update(SHA1_CTX *context, const uint8_t *data, size_t len)
 {
-    uint32_t i, j;
+    uint64_t i, j;
 
     _DIAGASSERT(context != 0);
     _DIAGASSERT(data != 0);
 
     j = context->count[0];
     if ((context->count[0] += len << 3) < j)
-	context->count[1] += (len>>29)+1;
+	context->count[1]++;
+    context->count[1] += (uint32_t)(len >> 29);
     j = (j >> 3) & 63;
     if ((j + len) > 63) {
 	(void)memcpy(&context->buffer[j], data, (i = 64-j));