Index: libcxxabi/src/demangle/Utility.h
===================================================================
--- libcxxabi/src/demangle/Utility.h
+++ libcxxabi/src/demangle/Utility.h
@@ -167,7 +167,8 @@
   void setCurrentPosition(size_t NewPos) { CurrentPosition = NewPos; }
 
   char back() const {
-    return CurrentPosition ? Buffer[CurrentPosition - 1] : '\0';
+    assert(CurrentPosition);
+    return Buffer[CurrentPosition - 1];
   }
 
   bool empty() const { return CurrentPosition == 0; }
Index: llvm/include/llvm/Demangle/Utility.h
===================================================================
--- llvm/include/llvm/Demangle/Utility.h
+++ llvm/include/llvm/Demangle/Utility.h
@@ -167,7 +167,8 @@
   void setCurrentPosition(size_t NewPos) { CurrentPosition = NewPos; }
 
   char back() const {
-    return CurrentPosition ? Buffer[CurrentPosition - 1] : '\0';
+    assert(CurrentPosition);
+    return Buffer[CurrentPosition - 1];
   }
 
   bool empty() const { return CurrentPosition == 0; }