diff --git a/src/plugins/clangformat/clangformatbaseindenter.cpp b/src/plugins/clangformat/clangformatbaseindenter.cpp
index c295a8a650a..a53eb50adb2 100644
--- a/src/plugins/clangformat/clangformatbaseindenter.cpp
+++ b/src/plugins/clangformat/clangformatbaseindenter.cpp
@@ -357,8 +357,10 @@ TextEditor::Replacements ClangFormatBaseIndenter::replacements(QByteArray buffer
     adjustFormatStyleForLineBreak(style, replacementsToKeep);
     if (typedChar == QChar::Null) {
         if (replacementsToKeep == ReplacementsToKeep::IndentAndBefore) {
-            buffer.insert(utf8Offset - 1, " //");
-            utf8Offset += 3;
+            if (utf8Offset > 0) {
+                buffer.insert(utf8Offset - 1, " //");
+                utf8Offset += 3;
+            }
             utf8Length += forceIndentWithExtraText(buffer,
                                                    cursorPositionInEditor < 0
                                                        ? endBlock
diff --git a/src/plugins/clangformat/clangformatindenter.cpp b/src/plugins/clangformat/clangformatindenter.cpp
index ef9dbf5d1ca..42cedb7b6c9 100644
--- a/src/plugins/clangformat/clangformatindenter.cpp
+++ b/src/plugins/clangformat/clangformatindenter.cpp
@@ -84,7 +84,10 @@ Utils::optional<TabSettings> ClangFormatIndenter::tabSettings() const
 
 int ClangFormatIndenter::lastSaveRevision() const
 {
-    return qobject_cast<TextEditor::TextDocumentLayout *>(m_doc->documentLayout())->lastSaveRevision;
+    auto *layout = qobject_cast<TextEditor::TextDocumentLayout *>(m_doc->documentLayout());
+    if (!layout)
+        return 0;
+    return layout->lastSaveRevision;
 }
 
 bool ClangFormatIndenter::formatOnSave() const