diff --git a/packages/block-library/src/template-part/editor.scss b/packages/block-library/src/template-part/editor.scss
index cfdf9b310fd8ad..af52ef32a67721 100644
--- a/packages/block-library/src/template-part/editor.scss
+++ b/packages/block-library/src/template-part/editor.scss
@@ -89,3 +89,18 @@
 		box-shadow: 0 0 0 $border-width var(--wp-admin-theme-color);
 	}
 }
+
+// Ensures a border is present when a child block is selected.
+.block-editor-block-list__block[data-type="core/template-part"] {
+	&.is-selected,
+	&.has-child-selected {
+		&::after {
+			top: $border-width;
+			bottom: $border-width;
+			left: $border-width;
+			right: $border-width;
+			border-radius: $radius-block-ui - $border-width; // Border is outset, so so subtract the width to achieve correct radius.
+			box-shadow: 0 0 0 $border-width $gray-900;
+		}
+	}
+}