diff --git a/src/wp-content/themes/twentynineteen/style-editor.css b/src/wp-content/themes/twentynineteen/style-editor.css
index 54487026e2..54575e038b 100644
--- a/src/wp-content/themes/twentynineteen/style-editor.css
+++ b/src/wp-content/themes/twentynineteen/style-editor.css
@@ -1605,3 +1605,9 @@ ul.wp-block-archives li ul,
   padding-right: 0;
   width: 100%;
 }
+
+/** === Post Author Block === */
+.avatar,
+.wp-block-post-author__avatar img {
+  border-radius: 100%;
+}
diff --git a/src/wp-content/themes/twentynineteen/style-editor.scss b/src/wp-content/themes/twentynineteen/style-editor.scss
index ce8a2883f8..6bf5507d1b 100644
--- a/src/wp-content/themes/twentynineteen/style-editor.scss
+++ b/src/wp-content/themes/twentynineteen/style-editor.scss
@@ -1021,3 +1021,10 @@ $group-block-background__padding: $font__size_base;
 		width: 100%;
 	}
 }
+
+/** === Post Author Block === */
+
+.avatar,
+.wp-block-post-author__avatar img {
+	border-radius: 100%;
+}