diff --git a/src/wp-admin/includes/file.php b/src/wp-admin/includes/file.php
index b1ea3fba1bda2..091317669b9b6 100644
--- a/src/wp-admin/includes/file.php
+++ b/src/wp-admin/includes/file.php
@@ -1040,7 +1040,9 @@ function wp_handle_upload_error( &$file, $message ) {
 	// Set correct file permissions.
 	$stat  = stat( dirname( $new_file ) );
 	$perms = $stat['mode'] & 0000666;
-	chmod( $new_file, $perms );
+	if( function_exists('chmod') ) {
+		chmod( $new_file, $perms );
+	}
 
 	// Compute the URL.
 	$url = $uploads['url'] . "/$filename";
@@ -2019,7 +2021,9 @@ function copy_dir( $from, $to, $skip_list = array() ) {
 		if ( 'f' === $fileinfo['type'] ) {
 			if ( ! $wp_filesystem->copy( $from . $filename, $to . $filename, true, FS_CHMOD_FILE ) ) {
 				// If copy failed, chmod file to 0644 and try again.
-				$wp_filesystem->chmod( $to . $filename, FS_CHMOD_FILE );
+				if( function_exists('chmod') ) {
+					$wp_filesystem->chmod( $to . $filename, FS_CHMOD_FILE );
+				}
 
 				if ( ! $wp_filesystem->copy( $from . $filename, $to . $filename, true, FS_CHMOD_FILE ) ) {
 					return new WP_Error( 'copy_failed_copy_dir', __( 'Could not copy file.' ), $to . $filename );
diff --git a/src/wp-admin/plugins.php b/src/wp-admin/plugins.php
index 339056b28278d..f36630f5cba9e 100644
--- a/src/wp-admin/plugins.php
+++ b/src/wp-admin/plugins.php
@@ -189,7 +189,9 @@
 				error_reporting( E_CORE_ERROR | E_CORE_WARNING | E_COMPILE_ERROR | E_ERROR | E_WARNING | E_PARSE | E_USER_ERROR | E_USER_WARNING | E_RECOVERABLE_ERROR );
 			}
 
-			ini_set( 'display_errors', true ); // Ensure that fatal errors are displayed.
+			if ( function_exists( 'ini_set' ) ) {
+				ini_set( 'display_errors', true ); // Ensure that fatal errors are displayed.
+			}
 			// Go back to "sandbox" scope so we get the same errors as before.
 			plugin_sandbox_scrape( $plugin );
 			/** This action is documented in wp-admin/includes/plugin.php */
diff --git a/src/wp-admin/update.php b/src/wp-admin/update.php
index 090c37cfc4dfe..541947158b8f6 100644
--- a/src/wp-admin/update.php
+++ b/src/wp-admin/update.php
@@ -96,7 +96,9 @@
 			echo '<p>' . __( 'Plugin failed to reactivate due to a fatal error.' ) . '</p>';
 
 			error_reporting( E_CORE_ERROR | E_CORE_WARNING | E_COMPILE_ERROR | E_ERROR | E_WARNING | E_PARSE | E_USER_ERROR | E_USER_WARNING | E_RECOVERABLE_ERROR );
-			ini_set( 'display_errors', true ); // Ensure that fatal errors are displayed.
+			if ( function_exists( 'ini_set' ) ) {
+				ini_set( 'display_errors', true ); // Ensure that fatal errors are displayed.
+			}
 			wp_register_plugin_realpath( WP_PLUGIN_DIR . '/' . $plugin );
 			include WP_PLUGIN_DIR . '/' . $plugin;
 		}
diff --git a/src/wp-includes/PHPMailer/PHPMailer.php b/src/wp-includes/PHPMailer/PHPMailer.php
index 31731594f12ec..197e5e6e32f85 100644
--- a/src/wp-includes/PHPMailer/PHPMailer.php
+++ b/src/wp-includes/PHPMailer/PHPMailer.php
@@ -1946,7 +1946,9 @@ protected function mailSend($header, $body)
                 $params = sprintf('-f%s', $this->Sender);
             }
             $old_from = ini_get('sendmail_from');
-            ini_set('sendmail_from', $this->Sender);
+				if ( function_exists('ini_set') ) {
+            	ini_set('sendmail_from', $this->Sender);
+				}
         }
         $result = false;
         if ($this->SingleTo && count($toArr) > 1) {
@@ -1969,7 +1971,9 @@ protected function mailSend($header, $body)
             $this->doCallback($result, $this->to, $this->cc, $this->bcc, $this->Subject, $body, $this->From, []);
         }
         if (isset($old_from)) {
-            ini_set('sendmail_from', $old_from);
+				if ( function_exists('ini_set') ) {
+            	ini_set('sendmail_from', $old_from);
+				}
         }
         if (!$result) {
             throw new Exception($this->lang('instantiate'), self::STOP_CRITICAL);
diff --git a/src/wp-includes/default-constants.php b/src/wp-includes/default-constants.php
index acfc878fb7138..519986f0a792f 100644
--- a/src/wp-includes/default-constants.php
+++ b/src/wp-includes/default-constants.php
@@ -68,7 +68,9 @@ function wp_initial_constants() {
 	// Set memory limits.
 	$wp_limit_int = wp_convert_hr_to_bytes( WP_MEMORY_LIMIT );
 	if ( -1 !== $current_limit_int && ( -1 === $wp_limit_int || $wp_limit_int > $current_limit_int ) ) {
-		ini_set( 'memory_limit', WP_MEMORY_LIMIT );
+		if ( function_exists( 'ini_set' ) ) {
+			ini_set( 'memory_limit', WP_MEMORY_LIMIT );
+		}
 	}
 
 	if ( ! isset( $blog_id ) ) {
diff --git a/src/wp-includes/functions.php b/src/wp-includes/functions.php
index 7e46dd53cab2d..a46bb346cff56 100644
--- a/src/wp-includes/functions.php
+++ b/src/wp-includes/functions.php
@@ -7883,13 +7883,13 @@ function wp_raise_memory_limit( $context = 'admin' ) {
 	$filtered_limit_int = wp_convert_hr_to_bytes( $filtered_limit );
 
 	if ( -1 === $filtered_limit_int || ( $filtered_limit_int > $wp_max_limit_int && $filtered_limit_int > $current_limit_int ) ) {
-		if ( false !== ini_set( 'memory_limit', $filtered_limit ) ) {
+		if ( function_exists( 'ini_set' ) && false !== ini_set( 'memory_limit', $filtered_limit ) ) {
 			return $filtered_limit;
 		} else {
 			return false;
 		}
 	} elseif ( -1 === $wp_max_limit_int || $wp_max_limit_int > $current_limit_int ) {
-		if ( false !== ini_set( 'memory_limit', $wp_max_limit ) ) {
+		if ( function_exists( 'ini_set' ) && false !== ini_set( 'memory_limit', $wp_max_limit ) ) {
 			return $wp_max_limit;
 		} else {
 			return false;
diff --git a/src/wp-includes/load.php b/src/wp-includes/load.php
index 5066cd16ee341..632b2d0c3d532 100644
--- a/src/wp-includes/load.php
+++ b/src/wp-includes/load.php
@@ -585,9 +585,13 @@ function wp_debug_mode() {
 		error_reporting( E_ALL );
 
 		if ( WP_DEBUG_DISPLAY ) {
-			ini_set( 'display_errors', 1 );
+			if ( function_exists( 'ini_set' ) ) {
+				ini_set( 'display_errors', 1 );
+			}
 		} elseif ( null !== WP_DEBUG_DISPLAY ) {
-			ini_set( 'display_errors', 0 );
+			if ( function_exists( 'ini_set' ) ) {
+				ini_set( 'display_errors', 0 );
+			}
 		}
 
 		if ( in_array( strtolower( (string) WP_DEBUG_LOG ), array( 'true', '1' ), true ) ) {
@@ -599,8 +603,10 @@ function wp_debug_mode() {
 		}
 
 		if ( $log_path ) {
-			ini_set( 'log_errors', 1 );
-			ini_set( 'error_log', $log_path );
+			if ( function_exists( 'ini_set' ) ) {
+				ini_set( 'log_errors', 1 );
+				ini_set( 'error_log', $log_path );
+			}
 		}
 	} else {
 		error_reporting( E_CORE_ERROR | E_CORE_WARNING | E_COMPILE_ERROR | E_ERROR | E_WARNING | E_PARSE | E_USER_ERROR | E_USER_WARNING | E_RECOVERABLE_ERROR );
@@ -614,7 +620,9 @@ function wp_debug_mode() {
 		|| ( defined( 'WP_INSTALLING' ) && WP_INSTALLING )
 		|| wp_doing_ajax() || wp_is_json_request()
 	) {
-		ini_set( 'display_errors', 0 );
+		if ( function_exists( 'ini_set' ) ) {
+			ini_set( 'display_errors', 0 );
+		}
 	}
 }
 
diff --git a/src/wp-includes/pomo/po.php b/src/wp-includes/pomo/po.php
index a4e3cab4ef17a..4be50a567c175 100644
--- a/src/wp-includes/pomo/po.php
+++ b/src/wp-includes/pomo/po.php
@@ -21,7 +21,9 @@
  * which still use the old MacOS standalone `\r` as a line ending.
  * This fix should be revisited when PHP 9.0 is in alpha/beta.
  */
-@ini_set( 'auto_detect_line_endings', 1 ); // phpcs:ignore WordPress.PHP.NoSilencedErrors.Discouraged
+if ( function_exists( 'ini_set' ) ) {
+	@ini_set( 'auto_detect_line_endings', 1 ); // phpcs:ignore WordPress.PHP.NoSilencedErrors.Discouraged
+}
 
 /**
  * Routines for working with PO files