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
@@ -1624,6 +1624,9 @@
     /// Whether this function has extended parameter information.
     unsigned HasExtParameterInfos : 1;
 
+    /// Whether this function has extra bitfields for the prototype.
+    unsigned HasExtraBitfields : 1;
+
     /// Whether the function is variadic.
     unsigned Variadic : 1;
 
@@ -3798,13 +3801,12 @@
 
   /// 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. You must update
-  /// hasExtraBitfields in FunctionProtoType after adding extra data here.
+  /// alignment of subsequent objects in TrailingObjects.
   struct 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;
+    unsigned NumExceptionType = 0;
   };
 
 protected:
@@ -3998,6 +4000,10 @@
       Result.ExceptionSpec = ESI;
       return Result;
     }
+
+    bool requiresFunctionProtoTypeExtraBitfields() const {
+      return ExceptionSpec.Type == EST_Dynamic;
+    }
   };
 
 private:
@@ -4088,16 +4094,13 @@
     return getExceptionSpecSize(getExceptionSpecType(), getNumExceptions());
   }
 
-  /// Whether the trailing FunctionTypeExtraBitfields is present.
-  static bool hasExtraBitfields(ExceptionSpecificationType EST) {
-    // If the exception spec type is EST_Dynamic then we have > 0 exception
-    // types and the exact number is stored in FunctionTypeExtraBitfields.
-    return EST == EST_Dynamic;
-  }
-
   /// Whether the trailing FunctionTypeExtraBitfields is present.
   bool hasExtraBitfields() const {
-    return hasExtraBitfields(getExceptionSpecType());
+    assert((getExceptionSpecType() != EST_Dynamic ||
+            FunctionTypeBits.HasExtraBitfields) &&
+           "ExtraBitfields are required for given ExceptionSpecType");
+    return FunctionTypeBits.HasExtraBitfields;
+
   }
 
   bool hasExtQualifiers() const {
diff --git a/clang/lib/AST/ASTContext.cpp b/clang/lib/AST/ASTContext.cpp
--- a/clang/lib/AST/ASTContext.cpp
+++ b/clang/lib/AST/ASTContext.cpp
@@ -4451,8 +4451,7 @@
       QualType, SourceLocation, FunctionType::FunctionTypeExtraBitfields,
       FunctionType::ExceptionType, Expr *, FunctionDecl *,
       FunctionProtoType::ExtParameterInfo, Qualifiers>(
-      NumArgs, EPI.Variadic,
-      FunctionProtoType::hasExtraBitfields(EPI.ExceptionSpec.Type),
+      NumArgs, EPI.Variadic, EPI.requiresFunctionProtoTypeExtraBitfields(),
       ESH.NumExceptionType, ESH.NumExprPtr, ESH.NumFunctionDeclPtr,
       EPI.ExtParameterInfos ? NumArgs : 0,
       EPI.TypeQuals.hasNonFastQualifiers() ? 1 : 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
@@ -3213,12 +3213,15 @@
   FunctionTypeBits.Variadic = epi.Variadic;
   FunctionTypeBits.HasTrailingReturn = epi.HasTrailingReturn;
 
-  // Fill in the extra trailing bitfields if present.
-  if (hasExtraBitfields(epi.ExceptionSpec.Type)) {
+  if (epi.requiresFunctionProtoTypeExtraBitfields()) {
+    FunctionTypeBits.HasExtraBitfields = true;
     auto &ExtraBits = *getTrailingObjects<FunctionTypeExtraBitfields>();
-    ExtraBits.NumExceptionType = epi.ExceptionSpec.Exceptions.size();
+    ExtraBits = FunctionTypeExtraBitfields();
+  } else {
+    FunctionTypeBits.HasExtraBitfields = false;
   }
 
+
   // Fill in the trailing argument array.
   auto *argSlot = getTrailingObjects<QualType>();
   for (unsigned i = 0; i != getNumParams(); ++i) {
@@ -3229,6 +3232,9 @@
 
   // Fill in the exception type array if present.
   if (getExceptionSpecType() == EST_Dynamic) {
+    auto &ExtraBits = *getTrailingObjects<FunctionTypeExtraBitfields>();
+    ExtraBits.NumExceptionType = epi.ExceptionSpec.Exceptions.size();
+
     assert(hasExtraBitfields() && "missing trailing extra bitfields!");
     auto *exnSlot =
         reinterpret_cast<QualType *>(getTrailingObjects<ExceptionType>());