diff --git a/extensions/amp-facebook/1.0/base-element.js b/extensions/amp-facebook/1.0/base-element.js
index ca458cd7f427..4ab2f731e1e7 100644
--- a/extensions/amp-facebook/1.0/base-element.js
+++ b/extensions/amp-facebook/1.0/base-element.js
@@ -29,6 +29,7 @@ BaseElement['props'] = {
   'includeCommentParent': {
     attr: 'data-include-comment-parent',
     type: 'boolean',
+    default: false,
   },
   'showText': {attr: 'data-show-text'},
   // -comments
diff --git a/extensions/amp-mathml/1.0/base-element.js b/extensions/amp-mathml/1.0/base-element.js
index e621128bb87c..723763e038c2 100644
--- a/extensions/amp-mathml/1.0/base-element.js
+++ b/extensions/amp-mathml/1.0/base-element.js
@@ -10,7 +10,7 @@ BaseElement['Component'] = BentoMathml;
 
 /** @override */
 BaseElement['props'] = {
-  'inline': {attr: 'inline', type: 'boolean'},
+  'inline': {attr: 'inline', type: 'boolean', default: false},
   'formula': {attr: 'data-formula'},
   'title': {attr: 'title'},
 };
diff --git a/extensions/amp-soundcloud/1.0/base-element.js b/extensions/amp-soundcloud/1.0/base-element.js
index 3a2554e91b56..0e001f652d0a 100644
--- a/extensions/amp-soundcloud/1.0/base-element.js
+++ b/extensions/amp-soundcloud/1.0/base-element.js
@@ -19,7 +19,7 @@ BaseElement['props'] = {
   'playlistId': {attr: 'data-playlistid'},
   'secretToken': {attr: 'data-secret-token'},
   'trackId': {attr: 'data-trackid'},
-  'visual': {attr: 'data-visual', type: 'boolean'},
+  'visual': {attr: 'data-visual', type: 'boolean', default: false},
 };
 
 /** @override */