diff --git a/features/plugin-activate.feature b/features/plugin-activate.feature
index 9264e004..10b47054 100644
--- a/features/plugin-activate.feature
+++ b/features/plugin-activate.feature
@@ -80,3 +80,29 @@ Feature: Activate WordPress plugins
       """
       Success: No plugins installed.
       """
+
+  @require-wp-5.2
+  Scenario: Activating a plugin that does not meet PHP minimum throws a warning
+    Given a wp-content/plugins/high-requirements.php file:
+      """
+      <?php
+      /**
+       * Plugin Name: High PHP Requirements
+       * Description: This is meant to not activate because PHP version is too low.
+       * Author: WP-CLI tests
+       * Requires PHP: 99.99
+       */
+       """
+    And I run `wp plugin deactivate --all`
+    And I run `php -r 'echo PHP_VERSION;'`
+    And save STDOUT as {PHP_VERSION}
+
+    When I try `wp plugin activate high-requirements`
+    Then STDERR should contain:
+      """
+      Failed to activate plugin. Current PHP version ({PHP_VERSION}) does not meet minimum requirements for High PHP Requirements. The plugin requires PHP 99.99.
+      """
+    And STDOUT should not contain:
+      """
+      1 out of 1
+      """
diff --git a/features/plugin.feature b/features/plugin.feature
index 63a87ea8..36a7583e 100644
--- a/features/plugin.feature
+++ b/features/plugin.feature
@@ -185,6 +185,7 @@ Feature: Manage WordPress plugins
     Given a WP install
     And a wp-content/plugins/network-only.php file:
       """
+      <?php
       // Plugin Name: Example Plugin
       // Network: true
       """
@@ -206,6 +207,7 @@ Feature: Manage WordPress plugins
     Given a WP multisite install
     And a wp-content/plugins/network-only.php file:
       """
+      <?php
       // Plugin Name: Example Plugin
       // Network: true
       """
@@ -537,7 +539,7 @@ Feature: Manage WordPress plugins
       """
     And the return code should be 0
 
-  @require-wp-47
+  @require-wp-4.7
   Scenario: Plugin hidden by "all_plugins" filter
     Given a WP install
     And these installed and active plugins:
diff --git a/src/Plugin_AutoUpdates_Command.php b/src/Plugin_AutoUpdates_Command.php
index fb37de2d..1be68e18 100644
--- a/src/Plugin_AutoUpdates_Command.php
+++ b/src/Plugin_AutoUpdates_Command.php
@@ -78,6 +78,9 @@ public function enable( $args, $assoc_args ) {
 		$disabled_only = Utils\get_flag_value( $assoc_args, 'disabled-only', false );
 
 		$args = $this->check_optional_args_and_all( $args, $all );
+		if ( ! $args ) {
+			return;
+		}
 
 		$plugins      = $this->fetcher->get_many( $args );
 		$auto_updates = get_site_option( static::SITE_OPTION );
@@ -152,6 +155,9 @@ public function disable( $args, $assoc_args ) {
 		$enabled_only = Utils\get_flag_value( $assoc_args, 'enabled-only', false );
 
 		$args = $this->check_optional_args_and_all( $args, $all );
+		if ( ! $args ) {
+			return;
+		}
 
 		$plugins      = $this->fetcher->get_many( $args );
 		$auto_updates = get_site_option( static::SITE_OPTION );
diff --git a/src/Plugin_Command.php b/src/Plugin_Command.php
index d9e3ae5d..35764df8 100644
--- a/src/Plugin_Command.php
+++ b/src/Plugin_Command.php
@@ -330,10 +330,18 @@ public function activate( $args, $assoc_args = array() ) {
 				deactivate_plugins( $plugin->file, false, false );
 			}
 
-			activate_plugin( $plugin->file, '', $network_wide );
-
-			$this->active_output( $plugin->name, $plugin->file, $network_wide, 'activate' );
-			$successes++;
+			$result = activate_plugin( $plugin->file, '', $network_wide );
+
+			if ( is_wp_error( $result ) ) {
+				$message = $result->get_error_message();
+				$message = preg_replace( '/<a\s[^>]+>.*<\/a>/im', '', $message );
+				$message = wp_strip_all_tags( $message );
+				$message = str_replace( 'Error: ', '', $message );
+				WP_CLI::warning( "Failed to activate plugin. {$message}" );
+			} else {
+				$this->active_output( $plugin->name, $plugin->file, $network_wide, 'activate' );
+				$successes++;
+			}
 		}
 
 		if ( ! $this->chained_command ) {
@@ -877,7 +885,7 @@ public function uninstall( $args, $assoc_args = array() ) {
 
 		$all = Utils\get_flag_value( $assoc_args, 'all', false );
 
-		// Check if plugin names of --all is passed.
+		// Check if plugin names or --all is passed.
 		$args = $this->check_optional_args_and_all( $args, $all, 'uninstall' );
 		if ( ! $args ) {
 			return;
@@ -1005,7 +1013,7 @@ public function is_active( $args, $assoc_args = array() ) {
 	public function delete( $args, $assoc_args = array() ) {
 		$all = Utils\get_flag_value( $assoc_args, 'all', false );
 
-		// Check if plugin names of --all is passed.
+		// Check if plugin names or --all is passed.
 		$args = $this->check_optional_args_and_all( $args, $all, 'delete' );
 		if ( ! $args ) {
 			return;
diff --git a/src/Theme_AutoUpdates_Command.php b/src/Theme_AutoUpdates_Command.php
index 84630d44..5dd3d9a5 100644
--- a/src/Theme_AutoUpdates_Command.php
+++ b/src/Theme_AutoUpdates_Command.php
@@ -78,6 +78,9 @@ public function enable( $args, $assoc_args ) {
 		$disabled_only = Utils\get_flag_value( $assoc_args, 'disabled-only', false );
 
 		$args = $this->check_optional_args_and_all( $args, $all );
+		if ( ! $args ) {
+			return;
+		}
 
 		$themes       = $this->fetcher->get_many( $args );
 		$auto_updates = get_site_option( static::SITE_OPTION );
@@ -152,6 +155,9 @@ public function disable( $args, $assoc_args ) {
 		$enabled_only = Utils\get_flag_value( $assoc_args, 'enabled-only', false );
 
 		$args = $this->check_optional_args_and_all( $args, $all );
+		if ( ! $args ) {
+			return;
+		}
 
 		$themes       = $this->fetcher->get_many( $args );
 		$auto_updates = get_site_option( static::SITE_OPTION );