diff --git a/WordPress/Sniffs/NamingConventions/PrefixAllGlobalsSniff.php b/WordPress/Sniffs/NamingConventions/PrefixAllGlobalsSniff.php
index 887d0408c9..74191df878 100644
--- a/WordPress/Sniffs/NamingConventions/PrefixAllGlobalsSniff.php
+++ b/WordPress/Sniffs/NamingConventions/PrefixAllGlobalsSniff.php
@@ -626,6 +626,11 @@ public function process_parameters( $stackPtr, $group_name, $matched_content, $p
 				return;
 			}
 
+			if ( strpos( $raw_content, '\\' ) !== false ) {
+				// Namespaced or unreachable constant.
+				return;
+			}
+
 			$data       = array( 'Global constants defined' );
 			$error_code = 'NonPrefixedConstantFound';
 		} else {
diff --git a/WordPress/Tests/NamingConventions/PrefixAllGlobalsUnitTest.1.inc b/WordPress/Tests/NamingConventions/PrefixAllGlobalsUnitTest.1.inc
index d8562e2eb3..2c9ca83f96 100644
--- a/WordPress/Tests/NamingConventions/PrefixAllGlobalsUnitTest.1.inc
+++ b/WordPress/Tests/NamingConventions/PrefixAllGlobalsUnitTest.1.inc
@@ -13,3 +13,6 @@ const SOME_CONSTANT = 'value';
 class Example {}
 interface I_Example {}
 trait T_Example {}
+
+// Issue #1056.
+define( __NAMESPACE__ . '\PLUGIN_FILE', __FILE__ );
diff --git a/WordPress/Tests/NamingConventions/PrefixAllGlobalsUnitTest.inc b/WordPress/Tests/NamingConventions/PrefixAllGlobalsUnitTest.inc
index cc258a131a..44d8dbff69 100644
--- a/WordPress/Tests/NamingConventions/PrefixAllGlobalsUnitTest.inc
+++ b/WordPress/Tests/NamingConventions/PrefixAllGlobalsUnitTest.inc
@@ -306,3 +306,15 @@ do_action( 'acronym-action' ); // OK.
 apply_filters( 'acronym/filter', $var ); // OK.
 do_action( "acronym-action-{$acronym_filter_var}" ); // OK.
 apply_filters( 'acronym/filter-' . $acronym_filter_var ); // OK.
+
+// Issue #1056.
+define( 'SomeNameSpace\PLUGIN_FILE', __FILE__ ); // OK.
+define( '\OtherNameSpace\PLUGIN_FILE', __FILE__ ); // OK.
+// OK: unreachable constants.
+define( __NAMESPACE__ . '\PLUGIN_FILE', __FILE__ );
+define( '\PLUGIN_FILE', __FILE__ );
+
+namespace Testing {
+	define( 'MY' . __NAMESPACE__, __FILE__ ); // Error, not actually namespaced.
+	define( 'MY\\' . __NAMESPACE__, __FILE__ ); // OK, even though strangely setup, the constant is in a namespace.
+}
diff --git a/WordPress/Tests/NamingConventions/PrefixAllGlobalsUnitTest.php b/WordPress/Tests/NamingConventions/PrefixAllGlobalsUnitTest.php
index 108471574b..d23bc645e7 100644
--- a/WordPress/Tests/NamingConventions/PrefixAllGlobalsUnitTest.php
+++ b/WordPress/Tests/NamingConventions/PrefixAllGlobalsUnitTest.php
@@ -57,6 +57,7 @@ public function getErrorList( $testFile = 'PrefixAllGlobalsUnitTest.inc' ) {
 					230 => ( function_exists( '\array_column' ) ) ? 0 : 1,
 					234 => ( defined( '\E_DEPRECATED' ) ) ? 0 : 1,
 					238 => ( class_exists( '\IntlTimeZone' ) ) ? 0 : 1,
+					318  => 1,
 				);
 
 			case 'PrefixAllGlobalsUnitTest.1.inc':