diff --git a/lib/Sema/CSGen.cpp b/lib/Sema/CSGen.cpp
index e4c1e480d5134..4b31e87487d74 100644
--- a/lib/Sema/CSGen.cpp
+++ b/lib/Sema/CSGen.cpp
@@ -752,7 +752,10 @@ namespace {
       }
       
       Type paramTy = fnTy->getInput();
-      auto paramTupleTy = paramTy->castTo<TupleType>();
+      auto paramTupleTy = paramTy->getAs<TupleType>();
+      if (!paramTupleTy || paramTupleTy->getNumElements() != 2)
+        return false;
+      
       auto firstParamTy = paramTupleTy->getElement(0).getType();
       auto secondParamTy = paramTupleTy->getElement(1).getType();
       
diff --git a/validation-test/compiler_crashers_2_fixed/0036-rdar23719809.swift b/validation-test/compiler_crashers_2_fixed/0036-rdar23719809.swift
new file mode 100644
index 0000000000000..84684763144b2
--- /dev/null
+++ b/validation-test/compiler_crashers_2_fixed/0036-rdar23719809.swift
@@ -0,0 +1,12 @@
+// RUN: not %target-swift-frontend %s -parse
+
+// rdar://problem/23719809&23720006
+
+func ~=() {}
+func ~=(_: Int) {}
+func ~=(_: () -> ()) {}
+
+switch 0 {
+case 0:
+    break
+}