diff --git a/index.js b/index.js
index ce02993..ef804ec 100644
--- a/index.js
+++ b/index.js
@@ -5,10 +5,10 @@ const Transform = require('stream').Transform
 
 const SPEC_ALGORITHMS = ['sha256', 'sha384', 'sha512']
 
-const BASE64_REGEX = /[a-z0-9+/]+(?:=?=?)/i
+const BASE64_REGEX = /^[a-z0-9+/]+(?:=?=?)$/i
 const SRI_REGEX = /^([^-]+)-([^?]+)([?\S*]*)$/
 const STRICT_SRI_REGEX = /^([^-]+)-([A-Za-z0-9+/]+(?:=?=?))([?\x21-\x7E]*)$/
-const VCHAR_REGEX = /[\x21-\x7E]+/
+const VCHAR_REGEX = /^[\x21-\x7E]+$/
 
 class IntegrityMetadata {
   constructor (metadata, opts) {
@@ -75,7 +75,7 @@ class Integrity {
     const other = typeof integrity === 'string'
     ? integrity
     : stringify(integrity, opts)
-    return parse(`${this.toString()} ${other}`, opts)
+    return parse(`${this.toString(opts)} ${other}`, opts)
   }
 }