diff --git a/CMakeLists.txt b/CMakeLists.txt
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -1,7 +1,7 @@
 cmake_minimum_required(VERSION 3.5)
 
 set(KF5_VERSION "5.56.0") # handled by release scripts
-set(KF5_DEP_VERSION "5.56.0") # handled by release scripts
+set(KF5_DEP_VERSION "5.55.0") # handled by release scripts
 project(KTextEditor VERSION ${KF5_VERSION})
 
 # ECM setup
diff --git a/src/syntax/katehighlight.cpp b/src/syntax/katehighlight.cpp
--- a/src/syntax/katehighlight.cpp
+++ b/src/syntax/katehighlight.cpp
@@ -115,6 +115,15 @@
      */
     auto definitions = definition().includedDefinitions();
 
+    // it's possible to not have any defintions with malformed file
+    if (definitions.isEmpty()) {
+        m_properties.resize(1);
+        m_propertiesForFormat.push_back(&m_properties[0]);
+        m_formats.resize(1);
+        m_formatsIdToIndex.insert(std::make_pair(m_formats[0].id(), 0));
+        return;
+    }
+
     /**
      * first: handle only really included definitions
      */
@@ -251,7 +260,9 @@
 {
     // WE ATM assume ascending offset order
     Q_ASSERT(m_textLineToHighlight);
-    Q_ASSERT(format.isValid());
+    if (!format.isValid()) {
+        return;
+    }
 
     // get internal attribute, must exist
     const auto it = m_formatsIdToIndex.find(format.id());