Index: lib/AST/ASTContext.cpp
===================================================================
--- lib/AST/ASTContext.cpp
+++ lib/AST/ASTContext.cpp
@@ -2771,7 +2771,7 @@
 
   // Anything else must be a function type. Rebuild it with the new exception
   // specification.
-  const auto *Proto = cast<FunctionProtoType>(Orig);
+  const auto *Proto = Orig->getAs<FunctionProtoType>();
   return getFunctionType(
       Proto->getReturnType(), Proto->getParamTypes(),
       Proto->getExtProtoInfo().withExceptionSpec(ESI));
Index: test/AST/function-alias.cpp
===================================================================
--- test/AST/function-alias.cpp
+++ test/AST/function-alias.cpp
@@ -0,0 +1,14 @@
+// RUN: %clang_cc1 -std=c++17 -fsyntax-only %s
+
+// Verify that ASTContext::getFunctionTypeWithExceptionSpec (called through
+// ASTContext::hasSameFunctionTypeIgnoringExceptionSpec from
+// ExprEvaluatorBase::handleCallExpr in lib/AST/ExprConstant.cpp) does not crash
+// for a type alias.
+
+constexpr int f() noexcept { return 0; }
+
+using F = int();
+
+constexpr int g(F * p) { return p(); }
+
+constexpr int n = g(f);