diff --git a/lib/Sema/ConstraintSystem.cpp b/lib/Sema/ConstraintSystem.cpp
index 4d1dff495fdff..9100d34d24ba2 100644
--- a/lib/Sema/ConstraintSystem.cpp
+++ b/lib/Sema/ConstraintSystem.cpp
@@ -655,9 +655,9 @@ Optional<std::pair<unsigned, Expr *>> ConstraintSystem::getExprDepthAndParent(
   return None;
 }
 
-Type ConstraintSystem::openUnboundGenericType(UnboundGenericType *unbound,
-                                              ConstraintLocatorBuilder locator,
-                                              OpenedTypeMap &replacements) {
+Type
+ConstraintSystem::openUnboundGenericType(UnboundGenericType *unbound,
+                                         ConstraintLocatorBuilder locator) {
   auto unboundDecl = unbound->getDecl();
   auto parentTy = unbound->getParent();
   if (parentTy) {
@@ -667,6 +667,7 @@ Type ConstraintSystem::openUnboundGenericType(UnboundGenericType *unbound,
   }
 
   // Open up the generic type.
+  OpenedTypeMap replacements;
   openGeneric(unboundDecl->getDeclContext(), unboundDecl->getGenericSignature(),
               locator, replacements);
 
@@ -790,8 +791,7 @@ Type ConstraintSystem::openUnboundGenericType(
 
   type = type.transform([&](Type type) -> Type {
       if (auto unbound = type->getAs<UnboundGenericType>()) {
-        OpenedTypeMap replacements;
-        return openUnboundGenericType(unbound, locator, replacements);
+        return openUnboundGenericType(unbound, locator);
       }
 
       return type;
diff --git a/lib/Sema/ConstraintSystem.h b/lib/Sema/ConstraintSystem.h
index be05109c2e095..d458367f0f40b 100644
--- a/lib/Sema/ConstraintSystem.h
+++ b/lib/Sema/ConstraintSystem.h
@@ -3411,8 +3411,7 @@ class ConstraintSystem {
   ///
   /// \returns The opened type.
   Type openUnboundGenericType(UnboundGenericType *unbound,
-                              ConstraintLocatorBuilder locator,
-                              OpenedTypeMap &replacements);
+                              ConstraintLocatorBuilder locator);
 
   /// "Open" the given type by replacing any occurrences of unbound
   /// generic types with bound generic types with fresh type variables as