diff --git a/clang/include/clang/AST/Type.h b/clang/include/clang/AST/Type.h
--- a/clang/include/clang/AST/Type.h
+++ b/clang/include/clang/AST/Type.h
@@ -3949,11 +3949,20 @@
   /// A simple holder for various uncommon bits which do not fit in
   /// FunctionTypeBitfields. Aligned to alignof(void *) to maintain the
   /// alignment of subsequent objects in TrailingObjects.
-  struct alignas(void *) FunctionTypeExtraBitfields {
+  class alignas(void *) FunctionTypeExtraBitfields {
     /// The number of types in the exception specification.
     /// A whole unsigned is not needed here and according to
     /// [implimits] 8 bits would be enough here.
-    unsigned NumExceptionType = 0;
+    unsigned NumExceptionType : 16;
+
+  public:
+    FunctionTypeExtraBitfields() : NumExceptionType(0) {}
+
+    void setNumExceptionType(unsigned N) {
+      assert(N < 65536 && "Not enough bits to encode exceptions");
+      NumExceptionType = N;
+    }
+    unsigned getNumExceptionType() const { return NumExceptionType; }
   };
 
 protected:
@@ -4329,7 +4338,7 @@
   unsigned getNumExceptions() const {
     return getExceptionSpecType() == EST_Dynamic
                ? getTrailingObjects<FunctionTypeExtraBitfields>()
-                     ->NumExceptionType
+                     ->getNumExceptionType()
                : 0;
   }
 
diff --git a/clang/lib/AST/Type.cpp b/clang/lib/AST/Type.cpp
--- a/clang/lib/AST/Type.cpp
+++ b/clang/lib/AST/Type.cpp
@@ -3371,7 +3371,7 @@
   // Fill in the exception type array if present.
   if (getExceptionSpecType() == EST_Dynamic) {
     auto &ExtraBits = *getTrailingObjects<FunctionTypeExtraBitfields>();
-    ExtraBits.NumExceptionType = epi.ExceptionSpec.Exceptions.size();
+    ExtraBits.setNumExceptionType(epi.ExceptionSpec.Exceptions.size());
 
     assert(hasExtraBitfields() && "missing trailing extra bitfields!");
     auto *exnSlot =