diff --git a/lib/crypto/sha256.js b/lib/crypto/sha256.js
index 7333fc17..ae292dbd 100644
--- a/lib/crypto/sha256.js
+++ b/lib/crypto/sha256.js
@@ -18,14 +18,9 @@
 
 const DESC = Buffer.allocUnsafe(8);
 const BUFFER64 = Buffer.allocUnsafe(64);
-let K, PADDING;
-let ctx, mctx;
+const PADDING = Buffer.allocUnsafe(64);
 
-PADDING = Buffer.allocUnsafe(64);
-PADDING.fill(0);
-PADDING[0] = 0x80;
-
-K = [
+const K = [
   0x428a2f98, 0x71374491, 0xb5c0fbcf, 0xe9b5dba5,
   0x3956c25b, 0x59f111f1, 0x923f82a4, 0xab1c5ed5,
   0xd807aa98, 0x12835b01, 0x243185be, 0x550c7dc3,
@@ -44,6 +39,9 @@ K = [
   0x90befffa, 0xa4506ceb, 0xbef9a3f7, 0xc67178f2
 ];
 
+PADDING.fill(0);
+PADDING[0] = 0x80;
+
 /**
  * SHA256
  * @alias module:crypto/sha256.SHA256
@@ -341,8 +339,8 @@ function readU32(buf, offset) {
  * Context Helpers
  */
 
-ctx = new SHA256();
-mctx = new SHA256Hmac();
+const ctx = new SHA256();
+const mctx = new SHA256Hmac();
 
 /**
  * Hash buffer with sha256.