diff --git a/class-tgm-plugin-activation.php b/class-tgm-plugin-activation.php
index 5cd628fb..eaedb324 100755
--- a/class-tgm-plugin-activation.php
+++ b/class-tgm-plugin-activation.php
@@ -1406,6 +1406,8 @@ public function register( $plugin ) {
 				'force_deactivation' => false,   // Boolean.
 				'external_url'       => '',      // String.
 				'is_callable'        => '',      // String|Array.
+				'class_exists'       => '',      // String.
+				'is_defined'         => '',      // String.
 			);
 
 			// Prepare the received data.
@@ -1864,7 +1866,10 @@ public function is_plugin_installed( $slug ) {
 		 * @return bool True if active, false otherwise.
 		 */
 		public function is_plugin_active( $slug ) {
-			return ( ( ! empty( $this->plugins[ $slug ]['is_callable'] ) && is_callable( $this->plugins[ $slug ]['is_callable'] ) ) || is_plugin_active( $this->plugins[ $slug ]['file_path'] ) );
+			return ( ( ! empty( $this->plugins[ $slug ]['is_callable'] ) && is_callable( $this->plugins[ $slug ]['is_callable'] ) )
+				|| ( ! empty( $this->plugins[ $slug ]['class_exists'] ) && class_exists( $this->plugins[ $slug ]['class_exists'] ) )
+				|| ( ! empty( $this->plugins[ $slug ]['is_defined'] ) && defined( $this->plugins[ $slug ]['is_defined'] ) )
+				|| is_plugin_active( $this->plugins[ $slug ]['file_path'] ) );
 		}
 
 		/**
diff --git a/example.php b/example.php
index df6c93fb..fcd431c2 100755
--- a/example.php
+++ b/example.php
@@ -70,6 +70,8 @@ function my_theme_register_required_plugins() {
 			'force_deactivation' => false, // If true, plugin is deactivated upon theme switch, useful for theme-specific plugins.
 			'external_url'       => '', // If set, overrides default API URL and points to an external URL.
 			'is_callable'        => '', // If set, this callable will be be checked for availability to determine if a plugin is active.
+			'class_exists'       => '', // Same behavior as is_callable, this checks if a class exists to determine if a plugin is active.
+			'is_defined'         => '', // Same behavior as is_callable, this checks if a constant is defined to determine if a plugin is active.
 		),
 
 		// This is an example of how to include a plugin from an arbitrary external source in your theme.