diff --git a/lib/outputcomponents.php b/lib/outputcomponents.php
index 3ffed7cbd65..d7c1cdc559b 100644
--- a/lib/outputcomponents.php
+++ b/lib/outputcomponents.php
@@ -237,11 +237,11 @@ class user_picture implements renderable {
 
         foreach (self::$fields as $field) {
             if ($field === 'id') {
-                if (isset($record->{$idalias})) {
+                if (property_exists($record, $idalias)) {
                     $return->id = $record->{$idalias};
                 }
             } else {
-                if (isset($record->{$fieldprefix.$field})) {
+                if (property_exists($record, $fieldprefix.$field)) {
                     $return->{$field} = $record->{$fieldprefix.$field};
                 }
             }
@@ -249,7 +249,7 @@ class user_picture implements renderable {
         // add extra fields if not already there
         if ($extrafields) {
             foreach ($extrafields as $e) {
-                if ($e === 'id' or isset($return->{$e})) {
+                if ($e === 'id' or property_exists($return, $e)) {
                     continue;
                 }
                 $return->{$e} = $record->{$fieldprefix.$e};
diff --git a/lib/simpletest/testoutputcomponents.php b/lib/simpletest/testoutputcomponents.php
index 0ca721cc398..61f67086d35 100644
--- a/lib/simpletest/testoutputcomponents.php
+++ b/lib/simpletest/testoutputcomponents.php
@@ -85,4 +85,30 @@ class user_picture_test extends UnitTestCase {
         }
         $this->assertEqual($returned->custom1, 'Value of custom1');
     }
+
+    public function test_user_picture_fields_unaliasing_null() {
+        $fields = user_picture::fields();
+        $fields = array_map('trim', explode(',', $fields));
+
+        $fakerecord = new stdClass();
+        $fakerecord->aliasedid = 42;
+        foreach ($fields as $field) {
+            if ($field !== 'id') {
+                $fakerecord->{'prefix'.$field} = "Value of $field";
+            }
+        }
+        $fakerecord->prefixcustom1 = 'Value of custom1';
+        $fakerecord->prefiximagealt = null;
+
+        $returned = user_picture::unalias($fakerecord, array('custom1'), 'aliasedid', 'prefix');
+
+        $this->assertEqual($returned->id, 42);
+        $this->assertEqual($returned->imagealt, null);
+        foreach ($fields as $field) {
+            if ($field !== 'id' and $field !== 'imagealt') {
+                $this->assertEqual($returned->{$field}, "Value of $field");
+            }
+        }
+        $this->assertEqual($returned->custom1, 'Value of custom1');
+    }
 }