diff --git a/classes/controllers/FrmStylesController.php b/classes/controllers/FrmStylesController.php
index 8be5d031f0..077a1904b4 100644
--- a/classes/controllers/FrmStylesController.php
+++ b/classes/controllers/FrmStylesController.php
@@ -1348,6 +1348,11 @@ public static function get_form_style_class( $class, $style ) {
 		$frm_style = new FrmStyle( $style );
 		$style     = $frm_style->get_one();
 
+		if ( ! $style ) {
+			// The style was deleted, so use the default style.
+			$style = ( new FrmStyle( 'default' ) )->get_one();
+		}
+
 		if ( $style ) {
 			$class .= ' frm_style_' . $style->post_name;
 			self::maybe_add_rtl_class( $style, $class );
diff --git a/tests/phpunit/styles/test_FrmStylesController.php b/tests/phpunit/styles/test_FrmStylesController.php
index a80f158abd..ed7d7c75df 100644
--- a/tests/phpunit/styles/test_FrmStylesController.php
+++ b/tests/phpunit/styles/test_FrmStylesController.php
@@ -185,4 +185,16 @@ public function test_save() {
 		$updated_style = $frm_style->get_one();
 		$this->assertSame( $style->post_title . ' Updated', $updated_style->post_title );
 	}
+
+	public function test_get_form_style_class_falls_back_to_default_style_when_style_is_deleted() {
+		$default_style = ( new FrmStyle( 'default' ) )->get_one();
+		$this->assertNotEmpty( $default_style );
+
+		$deleted_style_id = $default_style->ID + 100000;
+		$this->assertNull( ( new FrmStyle( $deleted_style_id ) )->get_one() );
+
+		$class = FrmStylesController::get_form_style_class( ' with_frm_style', $deleted_style_id );
+
+		$this->assertSame( ' with_frm_style frm_style_' . $default_style->post_name, $class );
+	}
 }