diff --git a/packages/block-library/src/button/style.scss b/packages/block-library/src/button/style.scss
index 2e0c50205a1cb7..65df1b3f0d5043 100644
--- a/packages/block-library/src/button/style.scss
+++ b/packages/block-library/src/button/style.scss
@@ -62,8 +62,12 @@ $blocks-block__margin: 0.5em;
 	}
 
 	&.wp-block-button__width-100 {
-		margin-right: 0;
-		width: 100%;
+		width: calc(100% - #{ $blocks-block__margin });
+
+		&:only-child {
+			margin-right: 0;
+			width: 100%;
+		}
 	}
 }