diff --git a/validation-test/compiler_crashers/28786-swift-typebase-getcontextsubstitutions-swift-declcontext-const-swift-genericenvi.swift b/validation-test/compiler_crashers/28786-swift-typebase-getcontextsubstitutions-swift-declcontext-const-swift-genericenvi.swift
new file mode 100644
index 0000000000000..345c2cd4d4734
--- /dev/null
+++ b/validation-test/compiler_crashers/28786-swift-typebase-getcontextsubstitutions-swift-declcontext-const-swift-genericenvi.swift
@@ -0,0 +1,11 @@
+// This source file is part of the Swift.org open source project
+// Copyright (c) 2014 - 2017 Apple Inc. and the Swift project authors
+// Licensed under Apache License v2.0 with Runtime Library Exception
+//
+// See https://swift.org/LICENSE.txt for license information
+// See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
+
+// RUN: not --crash %target-swift-frontend %s -emit-ir
+protocol P}typealias a:P}extension P{class a
+struct B{{{}}class a:A.a
+protocol A:a