diff --git a/src/plugins/texteditor/fontsettings.cpp b/src/plugins/texteditor/fontsettings.cpp
index 3cb58fd1282..54e384984b3 100644
--- a/src/plugins/texteditor/fontsettings.cpp
+++ b/src/plugins/texteditor/fontsettings.cpp
@@ -103,6 +103,7 @@ bool FontSettings::fromSettings(const FormatDescriptions &descriptions, const Qt
     m_fontSize = s->value(group + fontSizeKey, m_fontSize).toInt();
     m_fontZoom= s->value(group + fontZoomKey, m_fontZoom).toInt();
     m_lineSpacing = s->value(group + lineSpacingKey, m_lineSpacing).toInt();
+    QTC_ASSERT(m_lineSpacing >= 0, m_lineSpacing = 100);
     m_antialias = s->value(group + antialiasKey, DEFAULT_ANTIALIAS).toBool();
 
     if (s->contains(group + schemeFileNamesKey)) {
@@ -337,7 +338,7 @@ qreal FontSettings::lineSpacing() const
     QFont currentFont = font();
     currentFont.setPointSize(std::max(m_fontSize * m_fontZoom / 100, 1));
     qreal spacing = QFontMetricsF(currentFont).lineSpacing();
-    if (m_lineSpacing != 100)
+    if (QTC_GUARD(m_lineSpacing > 0) && m_lineSpacing != 100)
         spacing *= qreal(m_lineSpacing) / 100;
     return spacing;
 }
diff --git a/src/plugins/texteditor/texteditor.cpp b/src/plugins/texteditor/texteditor.cpp
index 8ced95c0fc0..4d71d42c45b 100644
--- a/src/plugins/texteditor/texteditor.cpp
+++ b/src/plugins/texteditor/texteditor.cpp
@@ -5160,6 +5160,7 @@ void TextEditorWidgetPrivate::updateLineAnnotation(const PaintEventData &data,
             q->viewport()->update(annotationRect.rect.toAlignedRect());
     }
     m_annotationRects[data.block.blockNumber()] = newRects;
+    QTC_ASSERT(data.lineSpacing != 0, return);
     const int maxVisibleLines = data.viewportRect.height() / data.lineSpacing;
     if (m_annotationRects.size() >= maxVisibleLines * 2)
         scheduleCleanupAnnotationCache();