diff --git a/packages/block-library/src/post-author/block.json b/packages/block-library/src/post-author/block.json
index dde9320841820..d66498c8ee3df 100644
--- a/packages/block-library/src/post-author/block.json
+++ b/packages/block-library/src/post-author/block.json
@@ -64,6 +64,18 @@
 		},
 		"interactivity": {
 			"clientNavigation": true
+		},
+		"__experimentalBorder": {
+			"radius": true,
+			"color": true,
+			"width": true,
+			"style": true,
+			"__experimentalDefaultControls": {
+				"radius": true,
+				"color": true,
+				"width": true,
+				"style": true
+			}
 		}
 	},
 	"editorStyle": "wp-block-post-author-editor",
diff --git a/packages/block-library/src/post-author/style.scss b/packages/block-library/src/post-author/style.scss
index 0b2d63aab44f6..28fd4fad3cf5a 100644
--- a/packages/block-library/src/post-author/style.scss
+++ b/packages/block-library/src/post-author/style.scss
@@ -1,6 +1,7 @@
 .wp-block-post-author {
 	display: flex;
 	flex-wrap: wrap;
+	box-sizing: border-box;
 
 	&__byline {
 		width: 100%;