diff --git a/newspack-theme/sass/blocks/_blocks.scss b/newspack-theme/sass/blocks/_blocks.scss
index 1d184af85..973005cba 100755
--- a/newspack-theme/sass/blocks/_blocks.scss
+++ b/newspack-theme/sass/blocks/_blocks.scss
@@ -1070,6 +1070,13 @@ hr {
 			}
 		}
 	}
+
+	&__button-behavior-expand:not(.wp-block-search__searchfield-hidden) {
+		.wp-block-search__button {
+			border-top-left-radius: 0;
+			border-bottom-left-radius: 0;
+		}
+	}
 }
 
 //! Code
diff --git a/newspack-theme/sass/style-editor-base.scss b/newspack-theme/sass/style-editor-base.scss
index 6e040ad0c..ddf026ad3 100644
--- a/newspack-theme/sass/style-editor-base.scss
+++ b/newspack-theme/sass/style-editor-base.scss
@@ -721,6 +721,13 @@ div[data-align='full'] {
 			}
 		}
 	}
+
+	&__button-behavior-expand:not(.wp-block-search__searchfield-hidden) {
+		.wp-block-search__button {
+			border-top-left-radius: 0;
+			border-bottom-left-radius: 0;
+		}
+	}
 }
 
 /** === Code === */