diff --git a/core-blocks/gallery/edit.js b/core-blocks/gallery/edit.js
index 7d776823c02647..14267a27cd459b 100644
--- a/core-blocks/gallery/edit.js
+++ b/core-blocks/gallery/edit.js
@@ -263,7 +263,7 @@ class GalleryEdit extends Component {
 						</li>
 					) ) }
 					{ isSelected &&
-						<li className="blocks-gallery-item">
+						<li className="blocks-gallery-item has-add-item-button">
 							<FormFileUpload
 								multiple
 								isLarge
diff --git a/core-blocks/gallery/style.scss b/core-blocks/gallery/style.scss
index 6d51a93880593f..4a64369653ad1e 100644
--- a/core-blocks/gallery/style.scss
+++ b/core-blocks/gallery/style.scss
@@ -44,8 +44,8 @@
 	// Cropped
 	&.is-cropped .blocks-gallery-image,
 	&.is-cropped .blocks-gallery-item {
-      a,
-      img {
+		a,
+		img {
 			flex: 1;
 			width: 100%;
 			height: 100%;
@@ -74,6 +74,14 @@
 		}
 	}
 
+	// Make the "Add new Gallery item" button full-width (so it always appears
+	// below other items).
+	.blocks-gallery-item {
+		&.has-add-item-button {
+			width: 100%;
+		}
+	}
+
 	// Apply max-width to floated items that have no intrinsic width
 	[data-align="left"] &,
 	[data-align="right"] &,