diff --git a/lib/externallib.php b/lib/externallib.php
index 95039eecf0c..56144efcb3a 100644
--- a/lib/externallib.php
+++ b/lib/externallib.php
@@ -379,7 +379,7 @@ class external_api {
         $levels = context_helper::get_all_levels();
         if (!empty($param['contextid'])) {
             return context::instance_by_id($param['contextid'], IGNORE_MISSING);
-        } else if (!empty($param['contextlevel']) && !empty($param['instanceid'])) {
+        } else if (!empty($param['contextlevel']) && isset($param['instanceid'])) {
             $contextlevel = "context_".$param['contextlevel'];
             if (!array_search($contextlevel, $levels)) {
                 throw new invalid_parameter_exception('Invalid context level = '.$param['contextlevel']);
diff --git a/lib/tests/externallib_test.php b/lib/tests/externallib_test.php
index 369c342b466..1012a6d6053 100644
--- a/lib/tests/externallib_test.php
+++ b/lib/tests/externallib_test.php
@@ -169,6 +169,11 @@ class core_externallib_testcase extends advanced_testcase {
             $this->assertInstanceOf('invalid_parameter_exception', $e);
         }
 
+        // Tests for context with instanceid equal to 0 (System context).
+        $realcontext = context_system::instance();
+        $fetchedcontext = test_exernal_api::get_context_wrapper(array("contextlevel" => "system", "instanceid" => 0));
+        $this->assertEquals($realcontext, $fetchedcontext);
+
         // Passing wrong level.
         $this->setExpectedException('invalid_parameter_exception');
         $fetchedcontext = test_exernal_api::get_context_wrapper(array("contextlevel" => "random", "instanceid" => $course->id));