diff --git a/lib/primitives/address.js b/lib/primitives/address.js
index 20ad7a84..bade0c52 100644
--- a/lib/primitives/address.js
+++ b/lib/primitives/address.js
@@ -881,18 +881,18 @@ Address.getType = function getType(prefix, network) {
  */
 
 function isMixedCase(str) {
-  let upper = false;
   let lower = false;
+  let upper = false;
 
   for (let i = 0; i < str.length; i++) {
     let ch = str.charCodeAt(i);
 
     if (ch & 32)
-      upper = true;
-    else
       lower = true;
+    else
+      upper = true;
 
-    if (upper && lower)
+    if (lower && upper)
       return true;
   }