diff --git a/src/widgets/helper/NotebookTab.cpp b/src/widgets/helper/NotebookTab.cpp
index 886366d5e..5a6660639 100644
--- a/src/widgets/helper/NotebookTab.cpp
+++ b/src/widgets/helper/NotebookTab.cpp
@@ -318,7 +318,7 @@ void NotebookTab::removeHighlightSources(const HighlightSources &toRemove)
 
     if (!this->highlightSources_.highlightedSource.empty())
     {
-        // keep HighlightState::Highlighted
+        assert(this->highlightState_ == HighlightState::Highlighted);
         return;
     }
 
@@ -338,6 +338,8 @@ void NotebookTab::removeHighlightSources(const HighlightSources &toRemove)
             this->update();
         }
     }
+
+    assert(this->highlightState_ != HighlightState::Highlighted);
 }
 
 void NotebookTab::copyHighlightStateAndSourcesFrom(const NotebookTab *sourceTab)