diff --git a/lib/mixins/properties-changed.js b/lib/mixins/properties-changed.js
index d200a3dffc..22766a3164 100644
--- a/lib/mixins/properties-changed.js
+++ b/lib/mixins/properties-changed.js
@@ -134,10 +134,12 @@ export const PropertiesChanged = dedupingMixin(
       if (!this.hasOwnProperty('__dataAttributes')) {
         this.__dataAttributes = Object.assign({}, this.__dataAttributes);
       }
-      if (!this.__dataAttributes[property]) {
-        const attr = this.constructor.attributeNameForProperty(property);
+      let attr = this.__dataAttributes[property];
+      if (!attr) {
+        attr = this.constructor.attributeNameForProperty(property);
         this.__dataAttributes[attr] = property;
       }
+      return attr;
     }
 
     /**
diff --git a/lib/mixins/properties-mixin.js b/lib/mixins/properties-mixin.js
index 06fe449d38..9420e79769 100644
--- a/lib/mixins/properties-mixin.js
+++ b/lib/mixins/properties-mixin.js
@@ -122,7 +122,7 @@ export const PropertiesMixin = dedupingMixin(superClass => {
      if (!this.hasOwnProperty('__observedAttributes')) {
        register(this.prototype);
        const props = this._properties;
-       this.__observedAttributes = props ? Object.keys(props).map(p => this.attributeNameForProperty(p)) : [];
+       this.__observedAttributes = props ? Object.keys(props).map(p => this.prototype._addPropertyToAttributeMap(p)) : [];
      }
      return this.__observedAttributes;
    }
diff --git a/test/unit/disable-upgrade.html b/test/unit/disable-upgrade.html
index ff705f7e9f..158935b9cc 100644
--- a/test/unit/disable-upgrade.html
+++ b/test/unit/disable-upgrade.html
@@ -271,6 +271,25 @@ <h2 id="element">[[prop]]</h2>
   </script>
 </dom-module>
 
+<script type="module">
+  import { Polymer } from '../../lib/legacy/polymer-fn.js';
+  Polymer({
+    is: 'x-disabled-camel',
+    properties: {
+      camelCaseProperty: Boolean,
+      bootedCorrectly: {
+        type: Boolean,
+        value: false
+      }
+    },
+    attached() {
+      if (this.camelCaseProperty) {
+        this.bootedCorrectly = true;
+      }
+    }
+  });
+</script>
+
   <script type="module">
 import '../../lib/mixins/disable-upgrade-mixin.js';
 import {flush} from '../../lib/utils/flush.js';
@@ -433,6 +452,14 @@ <h2 id="element">[[prop]]</h2>
     assert.ok(el.$.disabledBoundEl.wasDisconnected);
   });
 
+  test('elements with camelCase properties initialize correctly after being enabled', function() {
+    const div = document.createElement('div');
+    div.innerHTML = `<x-disabled-camel disable-upgrade camel-case-property></x-disabled-camel>`;
+    const camel = div.querySelector('x-disabled-camel');
+    document.body.appendChild(div);
+    camel.removeAttribute('disable-upgrade');
+    assert.ok(camel.bootedCorrectly);
+  });
 
 });