diff --git a/features/search-replace.feature b/features/search-replace.feature
index ebcf4587e..d01c25828 100644
--- a/features/search-replace.feature
+++ b/features/search-replace.feature
@@ -174,6 +174,14 @@ Feature: Do global search/replace
   Scenario: Regex search/replace with a incorrect `--regex-flags`
     Given a WP install
     When I try `wp search-replace '(Hello)\s(world)' '$2, $1' --regex --regex-flags='kppr'`
+    Then STDERR should contain:
+      """
+      (Hello)\s(world)
+      """
+    And STDERR should contain:
+      """
+      kppr
+      """
     And the return code should be 1
 
   Scenario: Search and replace within theme mods
@@ -355,10 +363,21 @@ Feature: Do global search/replace
       http://example.jp
       """
 
+    When I run `wp search-replace 'http://example.jp/' 'http://example.com/' wp_options --regex-delimiter='/'`
+    Then STDOUT should be a table containing rows:
+      | Table      | Column       | Replacements | Type       |
+      | wp_options | option_value | 2            | PHP        |
+
+    When I run `wp option get home`
+    Then STDOUT should be:
+      """
+      http://example.com
+      """
+
     When I try `wp search-replace 'HTTP://EXAMPLE.COM' 'http://example.jp/' wp_options --regex --regex-flags=i --regex-delimiter='1'`
     Then STDERR should be:
       """
-      Error: Incorrect regex delimiter.
+      Error: The regex '1HTTP://EXAMPLE.COM1i' fails.
       """
     And the return code should be 1
 
diff --git a/src/Search_Replace_Command.php b/src/Search_Replace_Command.php
index 270e96da0..6b875ead2 100644
--- a/src/Search_Replace_Command.php
+++ b/src/Search_Replace_Command.php
@@ -91,7 +91,7 @@ class Search_Replace_Command extends WP_CLI_Command {
 	 * : Pass PCRE modifiers to regex search-replace (e.g. 'i' for case-insensitivity).
 	 *
 	 * [--regex-delimiter=<regex-delimiter>]
-	 * : The delimiter to use for the regex. It must be escaped if it appears in the search string.
+	 * : The delimiter to use for the regex. It must be escaped if it appears in the search string. The default value is the result of `chr(1)`.
 	 *
 	 * [--format=<format>]
 	 * : Render output in a particular format.
@@ -139,18 +139,20 @@ public function __invoke( $args, $assoc_args ) {
 		$this->verbose         =  \WP_CLI\Utils\get_flag_value( $assoc_args, 'verbose' );
 		$this->regex           =  \WP_CLI\Utils\get_flag_value( $assoc_args, 'regex' );
 		$this->regex_flags     =  \WP_CLI\Utils\get_flag_value( $assoc_args, 'regex-flags' );
-		$this->regex_delimiter =  \WP_CLI\Utils\get_flag_value( $assoc_args, 'regex-delimiter', '/' );
+		$this->regex_delimiter =  \WP_CLI\Utils\get_flag_value( $assoc_args, 'regex-delimiter', chr( 1 ) );
 		$this->format          = \WP_CLI\Utils\get_flag_value( $assoc_args, 'format' );
 
-		// http://php.net/manual/en/reference.pcre.pattern.modifiers.php
-		if ( $this->regex_flags && ! preg_match( '/^(?!.*(.).*\1)[imsxeADSUXJu]+$/', $this->regex_flags ) ) {
-			WP_CLI::error( "Incorrect PCRE modifiers." );
-		}
-
-		if ( empty( $this->regex_delimiter ) ) {
-			$this->regex_delimiter = '/';
-		} elseif( ! preg_match( '/^[^0-9\\s]{1}$/', $this->regex_delimiter ) ) {
-			WP_CLI::error( "Incorrect regex delimiter." );
+		if ( ! empty( $this->regex ) ) {
+			if ( '' === $this->regex_delimiter ) {
+				$this->regex_delimiter = chr( 1 );
+			}
+			$search_regex = $this->regex_delimiter;
+			$search_regex .= $old;
+			$search_regex .= $this->regex_delimiter;
+			$search_regex .= $this->regex_flags;
+			if ( false === @preg_match( $search_regex, '' ) ) {
+				\WP_CLI::error( "The regex '$search_regex' fails." );
+			}
 		}
 
 		$this->skip_columns = explode( ',', \WP_CLI\Utils\get_flag_value( $assoc_args, 'skip-columns' ) );
diff --git a/src/WP_CLI/SearchReplacer.php b/src/WP_CLI/SearchReplacer.php
index 3aaed0e40..e4a508450 100644
--- a/src/WP_CLI/SearchReplacer.php
+++ b/src/WP_CLI/SearchReplacer.php
@@ -84,7 +84,11 @@ private function _run( $data, $serialised, $recursion_level = 0, $visited_data =
 
 			else if ( is_string( $data ) ) {
 				if ( $this->regex ) {
-					$data = preg_replace( "$this->regex_delimiter$this->from$this->regex_delimiter$this->regex_flags", $this->to, $data );
+					$search_regex = $this->regex_delimiter;
+					$search_regex .= $this->from;
+					$search_regex .= $this->regex_delimiter;
+					$search_regex .= $this->regex_flags;
+					$data = preg_replace( $search_regex, $this->to, $data );
 				} else {
 					$data = str_replace( $this->from, $this->to, $data );
 				}