diff --git a/packages/env/lib/wordpress.js b/packages/env/lib/wordpress.js
index 423547fad688b..bd3c4a23f8ff5 100644
--- a/packages/env/lib/wordpress.js
+++ b/packages/env/lib/wordpress.js
@@ -27,6 +27,30 @@ const { getCache, setCache } = require( './cache' );
  * @typedef {'development'|'tests'|'all'} WPEnvironmentSelection
  */
 
+/**
+ * Utility function to check if a WordPress version is lower than another version.
+ *
+ * This is a non-comprehensive check only intended for this usage, to avoid pulling in a full semver library.
+ * It only considers the major and minor portions of the version and ignores the rest. Additionally, it assumes that
+ * the minor version is always a single digit (i.e. 0-9).
+ *
+ * Do not use this function for general version comparison, as it will not work for all cases.
+ *
+ * @param {string} version        The version to check.
+ * @param {string} compareVersion The compare version to check whether the version is lower than.
+ * @return {boolean} True if the version is lower than the compare version, false otherwise.
+ */
+function isWPMajorMinorVersionLower( version, compareVersion ) {
+	const versionNumber = Number.parseFloat(
+		version.match( /^[0-9]+(\.[0-9]+)?/ )[ 0 ]
+	);
+	const compareVersionNumber = Number.parseFloat(
+		compareVersion.match( /^[0-9]+(\.[0-9]+)?/ )[ 0 ]
+	);
+
+	return versionNumber < compareVersionNumber;
+}
+
 /**
  * Checks a WordPress database connection. An error is thrown if the test is
  * unsuccessful.
@@ -51,11 +75,28 @@ async function checkDatabaseConnection( { dockerComposeConfigPath, debug } ) {
  * @param {Object}        spinner     A CLI spinner which indicates progress.
  */
 async function configureWordPress( environment, config, spinner ) {
+	let wpVersion = '';
+	try {
+		wpVersion = await readWordPressVersion(
+			config.env[ environment ].coreSource,
+			spinner,
+			config.debug
+		);
+	} catch ( err ) {
+		// Ignore error.
+	}
+
 	const installCommand = `wp core install --url="${ config.env[ environment ].config.WP_SITEURL }" --title="${ config.name }" --admin_user=admin --admin_password=password --admin_email=wordpress@example.com --skip-email`;
 
 	// -eo pipefail exits the command as soon as anything fails in bash.
 	const setupCommands = [ 'set -eo pipefail', installCommand ];
 
+	// WordPress versions below 5.1 didn't use proper spacing in wp-config.
+	const configAnchor =
+		wpVersion && isWPMajorMinorVersionLower( wpVersion, '5.1' )
+			? `"define('WP_DEBUG',"`
+			: `"define( 'WP_DEBUG',"`;
+
 	// Set wp-config.php values.
 	for ( let [ key, value ] of Object.entries(
 		config.env[ environment ].config
@@ -68,7 +109,7 @@ async function configureWordPress( environment, config, spinner ) {
 		// Add quotes around string values to work with multi-word strings better.
 		value = typeof value === 'string' ? `"${ value }"` : value;
 		setupCommands.push(
-			`wp config set ${ key } ${ value } --anchor="define( 'WP_DEBUG',"${
+			`wp config set ${ key } ${ value } --anchor=${ configAnchor }${
 				typeof value !== 'string' ? ' --raw' : ''
 			}`
 		);
@@ -98,6 +139,15 @@ async function configureWordPress( environment, config, spinner ) {
 		}
 	);
 
+	// WordPress versions below 5.1 didn't use proper spacing in wp-config.
+	// Additionally, WordPress versions below 5.4 used `dirname( __FILE__ )` instead of `__DIR__`.
+	let abspathDef = `define( 'ABSPATH', __DIR__ . '\\/' );`;
+	if ( wpVersion && isWPMajorMinorVersionLower( wpVersion, '5.1' ) ) {
+		abspathDef = `define('ABSPATH', dirname(__FILE__) . '\\/');`;
+	} else if ( wpVersion && isWPMajorMinorVersionLower( wpVersion, '5.4' ) ) {
+		abspathDef = `define( 'ABSPATH', dirname( __FILE__ ) . '\\/' );`;
+	}
+
 	// WordPress' PHPUnit suite expects a `wp-tests-config.php` in
 	// the directory that the test suite is contained within.
 	// Make sure ABSPATH points to the WordPress install.
@@ -106,7 +156,7 @@ async function configureWordPress( environment, config, spinner ) {
 		[
 			'sh',
 			'-c',
-			`sed -e "/^require.*wp-settings.php/d" -e "s/define( 'ABSPATH', __DIR__ . '\\/' );/define( 'ABSPATH', '\\/var\\/www\\/html\\/' );\\n\\tdefine( 'WP_DEFAULT_THEME', 'default' );/" /var/www/html/wp-config.php > /wordpress-phpunit/wp-tests-config.php`,
+			`sed -e "/^require.*wp-settings.php/d" -e "s/${ abspathDef }/define( 'ABSPATH', '\\/var\\/www\\/html\\/' );\\n\\tdefine( 'WP_DEFAULT_THEME', 'default' );/" /var/www/html/wp-config.php > /wordpress-phpunit/wp-tests-config.php`,
 		],
 		{
 			config: config.dockerComposeConfigPath,