diff --git a/src/SchemaReader.php b/src/SchemaReader.php
index 57de8edd..e385c1b4 100644
--- a/src/SchemaReader.php
+++ b/src/SchemaReader.php
@@ -861,7 +861,10 @@ private static function splitParts(DOMElement $node, string $typeName): array
             list($prefix, $name) = explode(':', $typeName);
         }
 
-        $namespace = $node->lookupNamespaceUri($prefix ?: '');
+        /**
+         * @psalm-suppress PossiblyNullArgument
+         */
+        $namespace = $node->lookupNamespaceUri($prefix);
 
         return array(
             $name,
diff --git a/tests/SchemaTest.php b/tests/SchemaTest.php
index 15920d9b..9c8a4826 100644
--- a/tests/SchemaTest.php
+++ b/tests/SchemaTest.php
@@ -6,9 +6,34 @@
 
 use GoetasWebservices\XML\XSDReader\Schema\Element\ElementDef;
 use GoetasWebservices\XML\XSDReader\Schema\Type\ComplexType;
+use GoetasWebservices\XML\XSDReader\Schema\Type\SimpleType;
 
 class SchemaTest extends BaseTest
 {
+    public function testWithXSDAsDefaultNamespace()
+    {
+        $xml = '
+        <schema xmlns="http://www.w3.org/2001/XMLSchema"
+            xmlns:ds="http://www.example.com"
+            targetNamespace="http://www.example.com"
+            elementFormDefault="qualified"> 
+
+            <simpleType name="CryptoBinary">
+              <restriction base="base64Binary"/>
+            </simpleType>
+            <simpleType name="LocalCryptoBinary">
+              <restriction base="ds:CryptoBinary"/>
+            </simpleType>
+        </schema>';
+        $schema = $this->reader->readString($xml);
+
+        $crypto = $schema->findType('CryptoBinary', 'http://www.example.com');
+        $this->assertInstanceOf(SimpleType::class, $crypto);
+
+        $localCrypto = $schema->findType('LocalCryptoBinary', 'http://www.example.com');
+        $this->assertInstanceOf(SimpleType::class, $localCrypto);
+    }
+
     /**
      * @expectedException \GoetasWebservices\XML\XSDReader\Exception\IOException
      * @expectedExceptionMessage Can't load the schema