diff --git a/.eslintrc.json b/.eslintrc.json
index aa47233f..fcce24d1 100644
--- a/.eslintrc.json
+++ b/.eslintrc.json
@@ -19,6 +19,6 @@
     "curly": "error",
     "eqeqeq": ["warn", "smart"],
     "no-var": "error",
-    "prefer-const": "warn"
+    "prefer-const": "error"
   }
 }
diff --git a/lib/exclusive-canonicalization.js b/lib/exclusive-canonicalization.js
index c08ec4f0..300492a5 100644
--- a/lib/exclusive-canonicalization.js
+++ b/lib/exclusive-canonicalization.js
@@ -192,7 +192,7 @@ ExclusiveCanonicalization.prototype.processInner = function (
 
   let i;
   let pfxCopy;
-  let ns = this.renderNs(
+  const ns = this.renderNs(
     node,
     prefixesInScope,
     defaultNs,
@@ -300,7 +300,7 @@ ExclusiveCanonicalization.prototype.process = function (node, options) {
    * If you have a PrefixList then use it and the ancestors to add the necessary namespaces
    */
   if (inclusiveNamespacesPrefixList) {
-    let prefixList =
+    const prefixList =
       inclusiveNamespacesPrefixList instanceof Array
         ? inclusiveNamespacesPrefixList
         : inclusiveNamespacesPrefixList.split(" ");
@@ -319,7 +319,7 @@ ExclusiveCanonicalization.prototype.process = function (node, options) {
     });
   }
 
-  let res = this.processInner(
+  const res = this.processInner(
     node,
     [],
     defaultNs,