diff --git a/autotests/syntaxrepository_test.cpp b/autotests/syntaxrepository_test.cpp
--- a/autotests/syntaxrepository_test.cpp
+++ b/autotests/syntaxrepository_test.cpp
@@ -252,6 +252,34 @@
         auto customTheme = repo.theme(QLatin1String("Test Theme"));
         QVERIFY(customTheme.isValid());
     }
+
+    void testEmptyDefinition()
+    {
+        Definition def;
+        QVERIFY(!def.isValid());
+        QVERIFY(def.filePath().isEmpty());
+        QVERIFY(def.name().isEmpty());
+        QVERIFY(def.translatedName().isEmpty());
+        QVERIFY(def.section().isEmpty());
+        QVERIFY(def.translatedSection().isEmpty());
+        QVERIFY(def.mimeTypes().isEmpty());
+        QVERIFY(def.extensions().isEmpty());
+        QCOMPARE(def.version(), 0);
+        QCOMPARE(def.priority(), 0);
+        QVERIFY(!def.isHidden());
+        QVERIFY(def.style().isEmpty());
+        QVERIFY(def.indenter().isEmpty());
+        QVERIFY(def.author().isEmpty());
+        QVERIFY(def.license().isEmpty());
+        QVERIFY(!def.indentationBasedFoldingEnabled());
+        QVERIFY(def.foldingIgnoreList().isEmpty());
+        QVERIFY(def.keywordLists().isEmpty());
+        QVERIFY(def.formats().isEmpty());
+        QVERIFY(def.includedDefinitions().isEmpty());
+
+        for (QChar c : QStringLiteral("\t !%&()*+,-./:;<=>?[\\]^{|}~"))
+            QVERIFY(def.isDelimiter(c));
+    }
 };
 }
 
diff --git a/src/lib/definition.cpp b/src/lib/definition.cpp
--- a/src/lib/definition.cpp
+++ b/src/lib/definition.cpp
@@ -284,10 +284,12 @@
 
 bool DefinitionData::load()
 {
+    if (fileName.isEmpty())
+        return false;
+
     if (isLoaded())
         return true;
 
-    Q_ASSERT(!fileName.isEmpty());
     QFile file(fileName);
     if (!file.open(QFile::ReadOnly))
         return false;