diff --git a/src/wp-includes/pomo/entry.php b/src/wp-includes/pomo/entry.php
index a750a944a9..b5e56ff28a 100644
--- a/src/wp-includes/pomo/entry.php
+++ b/src/wp-includes/pomo/entry.php
@@ -81,7 +81,7 @@ if ( ! class_exists( 'Translation_Entry', false ) ) :
 			}
 
 			// Prepend context and EOT, like in MO files
-			$key = ! $this->context ? $this->singular : $this->context . chr( 4 ) . $this->singular;
+			$key = ! $this->context ? $this->singular : $this->context . "\4" . $this->singular;
 			// Standardize on \n line endings
 			$key = str_replace( array( "\r\n", "\r" ), "\n", $key );
 
diff --git a/src/wp-includes/pomo/mo.php b/src/wp-includes/pomo/mo.php
index 44d8cdfc87..25b9e37a9f 100644
--- a/src/wp-includes/pomo/mo.php
+++ b/src/wp-includes/pomo/mo.php
@@ -124,12 +124,12 @@ if ( ! class_exists( 'MO', false ) ) :
 			// headers' msgid is an empty string
 			fwrite( $fh, pack( 'VV', 0, $current_addr ) );
 			$current_addr++;
-			$originals_table = chr( 0 );
+			$originals_table = "\0";
 
 			$reader = new POMO_Reader();
 
 			foreach ( $entries as $entry ) {
-				$originals_table .= $this->export_original( $entry ) . chr( 0 );
+				$originals_table .= $this->export_original( $entry ) . "\0";
 				$length           = $reader->strlen( $this->export_original( $entry ) );
 				fwrite( $fh, pack( 'VV', $length, $current_addr ) );
 				$current_addr += $length + 1; // account for the NULL byte after
@@ -138,10 +138,10 @@ if ( ! class_exists( 'MO', false ) ) :
 			$exported_headers = $this->export_headers();
 			fwrite( $fh, pack( 'VV', $reader->strlen( $exported_headers ), $current_addr ) );
 			$current_addr      += strlen( $exported_headers ) + 1;
-			$translations_table = $exported_headers . chr( 0 );
+			$translations_table = $exported_headers . "\0";
 
 			foreach ( $entries as $entry ) {
-				$translations_table .= $this->export_translations( $entry ) . chr( 0 );
+				$translations_table .= $this->export_translations( $entry ) . "\0";
 				$length              = $reader->strlen( $this->export_translations( $entry ) );
 				fwrite( $fh, pack( 'VV', $length, $current_addr ) );
 				$current_addr += $length + 1;
@@ -160,10 +160,10 @@ if ( ! class_exists( 'MO', false ) ) :
 			//TODO: warnings for control characters
 			$exported = $entry->singular;
 			if ( $entry->is_plural ) {
-				$exported .= chr( 0 ) . $entry->plural;
+				$exported .= "\0" . $entry->plural;
 			}
 			if ( $entry->context ) {
-				$exported = $entry->context . chr( 4 ) . $exported;
+				$exported = $entry->context . "\4" . $exported;
 			}
 			return $exported;
 		}
@@ -174,7 +174,7 @@ if ( ! class_exists( 'MO', false ) ) :
 		 */
 		function export_translations( $entry ) {
 			//TODO: warnings for control characters
-			return $entry->is_plural ? implode( chr( 0 ), $entry->translations ) : $entry->translations[0];
+			return $entry->is_plural ? implode( "\0", $entry->translations ) : $entry->translations[0];
 		}
 
 		/**
@@ -310,21 +310,21 @@ if ( ! class_exists( 'MO', false ) ) :
 		 */
 		function &make_entry( $original, $translation ) {
 			$entry = new Translation_Entry();
-			// look for context
-			$parts = explode( chr( 4 ), $original );
+			// Look for context, separated by \4.
+			$parts = explode( "\4", $original );
 			if ( isset( $parts[1] ) ) {
 				$original       = $parts[1];
 				$entry->context = $parts[0];
 			}
 			// look for plural original
-			$parts           = explode( chr( 0 ), $original );
+			$parts           = explode( "\0", $original );
 			$entry->singular = $parts[0];
 			if ( isset( $parts[1] ) ) {
 				$entry->is_plural = true;
 				$entry->plural    = $parts[1];
 			}
 			// plural translations are also separated by \0
-			$entry->translations = explode( chr( 0 ), $translation );
+			$entry->translations = explode( "\0", $translation );
 			return $entry;
 		}