Index: clang/include/clang/AST/Type.h
===================================================================
--- clang/include/clang/AST/Type.h
+++ clang/include/clang/AST/Type.h
@@ -1520,6 +1520,8 @@
     unsigned Kind : 8;
   };
 
+  enum { NumParamsBits = 16 };
+
   /// FunctionTypeBitfields store various bits belonging to FunctionProtoType.
   /// Only common bits are stored here. Additional uncommon bits are stored
   /// in a trailing object after FunctionProtoType.
@@ -1552,7 +1554,7 @@
     /// According to [implimits] 8 bits should be enough here but this is
     /// somewhat easy to exceed with metaprogramming and so we would like to
     /// keep NumParams as wide as reasonably possible.
-    unsigned NumParams : 16;
+    unsigned NumParams : NumParamsBits;
 
     /// The type of exception specification this function has.
     unsigned ExceptionSpecType : 4;
@@ -2360,6 +2362,11 @@
   ///        this type can have nullability because it is dependent.
   bool canHaveNullability(bool ResultIfUnknown = true) const;
 
+  /// @returns The maximum number of parameters for a function.
+  static constexpr unsigned getMaxNumParams() {
+    return (1u << NumParamsBits) - 1;
+  }
+
   /// Retrieve the set of substitutions required when accessing a member
   /// of the Objective-C receiver type that is declared in the given context.
   ///
Index: clang/include/clang/Basic/DiagnosticParseKinds.td
===================================================================
--- clang/include/clang/Basic/DiagnosticParseKinds.td
+++ clang/include/clang/Basic/DiagnosticParseKinds.td
@@ -326,6 +326,8 @@
 def err_argument_required_after_attribute : Error<
   "argument required after attribute">;
 def err_missing_param : Error<"expected parameter declarator">;
+def err_number_of_function_parameters_exceeded : Error<
+  "number of function parameters exceeded maximum of %0">, DefaultFatal;
 def err_missing_comma_before_ellipsis : Error<
   "C requires a comma prior to the ellipsis in a variadic function type">;
 def err_unexpected_typedef_ident : Error<
Index: clang/lib/Parse/ParseDecl.cpp
===================================================================
--- clang/lib/Parse/ParseDecl.cpp
+++ clang/lib/Parse/ParseDecl.cpp
@@ -6668,6 +6668,15 @@
 
     // If the next token is a comma, consume it and keep reading arguments.
   } while (TryConsumeToken(tok::comma));
+
+  // Avoid exceeding the maximum function parameters
+  // See https://bugs.llvm.org/show_bug.cgi?id=19607
+  if (ParamInfo.size() > Type::getMaxNumParams()) {
+    Diag(ParamInfo[Type::getMaxNumParams() - 1].IdentLoc,
+         diag::err_number_of_function_parameters_exceeded)
+        << Type::getMaxNumParams();
+    cutOffParsing();
+  }
 }
 
 /// [C90]   direct-declarator '[' constant-expression[opt] ']'
Index: clang/lib/Parse/ParseExprCXX.cpp
===================================================================
--- clang/lib/Parse/ParseExprCXX.cpp
+++ clang/lib/Parse/ParseExprCXX.cpp
@@ -1265,6 +1265,14 @@
 
       ParseParameterDeclarationClause(D, Attr, ParamInfo, EllipsisLoc);
 
+      // If the parameters could not be parsed stop processing. Proceeding is
+      // not an issue when the maximum scope depth is exceeded. But when the
+      // maximum number of parameters is exceeded the processing will still hit
+      // the assertion in FunctionProtoType's constructor.
+      // See https://bugs.llvm.org/show_bug.cgi?id=19607
+      if (Tok.is(tok::eof))
+        return ExprError();
+
       // For a generic lambda, each 'auto' within the parameter declaration
       // clause creates a template type parameter, so increment the depth.
       // If we've parsed any explicit template parameters, then the depth will
Index: clang/test/Parser/function_parameter_overflow.cpp
===================================================================
--- /dev/null
+++ clang/test/Parser/function_parameter_overflow.cpp
@@ -0,0 +1,11 @@
+// RUN: %clang_cc1 %s -fsyntax-only
+// RUN: not %clang_cc1 %s -fsyntax-only -DFAIL 2>&1 | FileCheck %s
+
+#include "parameter_overflow.h"
+
+void foo(I65535
+#ifdef FAIL
+, int
+#endif
+);
+// CHECK: fatal error: number of function parameters exceeded maximum of 65535
Index: clang/test/Parser/lambda_function_parameter_overflow.cpp
===================================================================
--- /dev/null
+++ clang/test/Parser/lambda_function_parameter_overflow.cpp
@@ -0,0 +1,11 @@
+// RUN: %clang_cc1 %s -fsyntax-only
+// RUN: not %clang_cc1 %s -fsyntax-only -DFAIL 2>&1 | FileCheck %s
+
+#include "parameter_overflow.h"
+
+auto foo = [](I65535
+#ifdef FAIL
+, int
+#endif
+){};
+// CHECK: fatal error: number of function parameters exceeded maximum of 65535
Index: clang/test/Parser/parameter_overflow.h
===================================================================
--- /dev/null
+++ clang/test/Parser/parameter_overflow.h
@@ -0,0 +1,9 @@
+#pragma once
+
+#define I10 int, int, int, int, int, int, int, int, int, int
+#define I50 I10, I10, I10, I10, I10
+#define I500 I50, I50, I50, I50, I50, I50, I50, I50, I50, I50
+#define I5000 I500, I500, I500, I500, I500, I500, I500, I500, I500, I500
+#define I60000 I5000, I5000, I5000, I5000, I5000, I5000, I5000, I5000, I5000, I5000, I5000, I5000
+
+#define  I65535 I60000, I5000, I500, I10, I10, I10, int, int, int, int, int