Index: clang/lib/Format/UnwrappedLineParser.cpp
===================================================================
--- clang/lib/Format/UnwrappedLineParser.cpp
+++ clang/lib/Format/UnwrappedLineParser.cpp
@@ -864,6 +864,10 @@
   if (AddLevels > 0u && Style.BreakBeforeBraces != FormatStyle::BS_Whitesmiths)
     Line->Level += AddLevels;
 
+  // Bail out if there are too many levels. Otherwise, the stack might overflow.
+  if (Line->Level > 300)
+    return;
+
   const bool SimpleBlock =
       parseLevel(Tok, CanContainBracedList, NextLBracesType, IfKind);