diff --git a/executable_semantics/BUILD b/executable_semantics/BUILD
index aa0d504e7bfd..ea2291dde895 100644
--- a/executable_semantics/BUILD
+++ b/executable_semantics/BUILD
@@ -32,7 +32,7 @@ cc_library(
     deps = [
         "//executable_semantics/ast:declaration",
         "//executable_semantics/ast:expression",
-        "//executable_semantics/ast:expression_or_field_list",
+        "//executable_semantics/ast:field_list",
         "//executable_semantics/interpreter",
     ],
 )
diff --git a/executable_semantics/ast/BUILD b/executable_semantics/ast/BUILD
index b981a553a3c1..99e88447dda8 100644
--- a/executable_semantics/ast/BUILD
+++ b/executable_semantics/ast/BUILD
@@ -24,9 +24,9 @@ cc_library(
 )
 
 cc_library(
-    name = "expression_or_field_list",
-    srcs = ["expression_or_field_list.cpp"],
-    hdrs = ["expression_or_field_list.h"],
+    name = "field_list",
+    srcs = ["field_list.cpp"],
+    hdrs = ["field_list.h"],
     deps = [":expression"],
 )
 
diff --git a/executable_semantics/ast/expression_or_field_list.cpp b/executable_semantics/ast/expression_or_field_list.cpp
deleted file mode 100644
index d3f0f8205b7b..000000000000
--- a/executable_semantics/ast/expression_or_field_list.cpp
+++ /dev/null
@@ -1,49 +0,0 @@
-// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
-// Exceptions. See /LICENSE for license information.
-// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
-
-#include "executable_semantics/ast/expression_or_field_list.h"
-
-namespace Carbon {
-
-auto MakeExp(Expression* exp) -> ExpOrFieldList* {
-  auto e = new ExpOrFieldList();
-  e->tag = ExpOrFieldListKind::Exp;
-  e->u.exp = exp;
-  return e;
-}
-
-auto MakeFieldList(std::list<std::pair<std::string, Expression*>>* fields)
-    -> ExpOrFieldList* {
-  auto e = new ExpOrFieldList();
-  e->tag = ExpOrFieldListKind::FieldList;
-  e->u.fields = fields;
-  return e;
-}
-
-auto MakeConsField(ExpOrFieldList* e1, ExpOrFieldList* e2) -> ExpOrFieldList* {
-  auto fields = new std::list<std::pair<std::string, Expression*>>();
-  switch (e1->tag) {
-    case ExpOrFieldListKind::Exp:
-      fields->push_back(std::make_pair("", e1->u.exp));
-      break;
-    case ExpOrFieldListKind::FieldList:
-      for (auto& field : *e1->u.fields) {
-        fields->push_back(field);
-      }
-      break;
-  }
-  switch (e2->tag) {
-    case ExpOrFieldListKind::Exp:
-      fields->push_back(std::make_pair("", e2->u.exp));
-      break;
-    case ExpOrFieldListKind::FieldList:
-      for (auto& field : *e2->u.fields) {
-        fields->push_back(field);
-      }
-      break;
-  }
-  return MakeFieldList(fields);
-}
-
-}  // namespace Carbon
diff --git a/executable_semantics/ast/expression_or_field_list.h b/executable_semantics/ast/expression_or_field_list.h
deleted file mode 100644
index b5054c7461ab..000000000000
--- a/executable_semantics/ast/expression_or_field_list.h
+++ /dev/null
@@ -1,32 +0,0 @@
-// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
-// Exceptions. See /LICENSE for license information.
-// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
-
-#ifndef EXECUTABLE_SEMANTICS_AST_EXPRESSION_OR_FIELD_LIST_H_
-#define EXECUTABLE_SEMANTICS_AST_EXPRESSION_OR_FIELD_LIST_H_
-
-#include <list>
-
-#include "executable_semantics/ast/expression.h"
-
-namespace Carbon {
-
-enum class ExpOrFieldListKind { Exp, FieldList };
-
-// This is used in the parsing of tuples and parenthesized expressions.
-struct ExpOrFieldList {
-  ExpOrFieldListKind tag;
-  union {
-    Expression* exp;
-    std::list<std::pair<std::string, Expression*>>* fields;
-  } u;
-};
-
-auto MakeExp(Expression* exp) -> ExpOrFieldList*;
-auto MakeFieldList(std::list<std::pair<std::string, Expression*>>* fields)
-    -> ExpOrFieldList*;
-auto MakeConsField(ExpOrFieldList* e1, ExpOrFieldList* e2) -> ExpOrFieldList*;
-
-}  // namespace Carbon
-
-#endif  // EXECUTABLE_SEMANTICS_AST_EXPRESSION_OR_FIELD_LIST_H_
diff --git a/executable_semantics/ast/field_list.cpp b/executable_semantics/ast/field_list.cpp
new file mode 100644
index 000000000000..96e730a83680
--- /dev/null
+++ b/executable_semantics/ast/field_list.cpp
@@ -0,0 +1,29 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+
+#include "executable_semantics/ast/field_list.h"
+
+namespace Carbon {
+
+auto MakeFieldList(std::list<std::pair<std::string, Expression*>>* fields)
+    -> FieldList* {
+  auto e = new FieldList();
+  e->fields = fields;
+  return e;
+}
+
+auto MakeConsField(FieldList* e1, FieldList* e2) -> FieldList* {
+  auto fields = new std::list<std::pair<std::string, Expression*>>();
+  for (auto& field : *e1->fields) {
+    fields->push_back(field);
+  }
+  for (auto& field : *e2->fields) {
+    fields->push_back(field);
+  }
+  auto result = MakeFieldList(fields);
+  result->has_explicit_comma = true;
+  return result;
+}
+
+}  // namespace Carbon
diff --git a/executable_semantics/ast/field_list.h b/executable_semantics/ast/field_list.h
new file mode 100644
index 000000000000..3d02b7dd7939
--- /dev/null
+++ b/executable_semantics/ast/field_list.h
@@ -0,0 +1,26 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+
+#ifndef EXECUTABLE_SEMANTICS_AST_FIELD_LIST_H_
+#define EXECUTABLE_SEMANTICS_AST_FIELD_LIST_H_
+
+#include <list>
+
+#include "executable_semantics/ast/expression.h"
+
+namespace Carbon {
+
+// This is used in the parsing of tuples and parenthesized expressions.
+struct FieldList {
+  std::list<std::pair<std::string, Expression*>>* fields;
+  bool has_explicit_comma = false;
+};
+
+auto MakeFieldList(std::list<std::pair<std::string, Expression*>>* fields)
+    -> FieldList*;
+auto MakeConsField(FieldList* e1, FieldList* e2) -> FieldList*;
+
+}  // namespace Carbon
+
+#endif  // EXECUTABLE_SEMANTICS_AST_FIELD_LIST_H_
diff --git a/executable_semantics/syntax.ypp b/executable_semantics/syntax.ypp
index 6523a62eb51d..4bb95de2969b 100644
--- a/executable_semantics/syntax.ypp
+++ b/executable_semantics/syntax.ypp
@@ -15,7 +15,7 @@
 
 %code requires {
 #include "executable_semantics/ast/declaration.h"
-#include "executable_semantics/ast/expression_or_field_list.h"
+#include "executable_semantics/ast/field_list.h"
 #include "executable_semantics/ast/function_definition.h"
 }
 
@@ -41,7 +41,7 @@ void yyerror(char* error) {
    std::list<Carbon::Declaration>* declaration_list;
    Carbon::Member* member;
    std::list<Carbon::Member*>* member_list;
-   Carbon::ExpOrFieldList* field_list;
+   Carbon::FieldList* field_list;
    std::pair<std::string, Carbon::Expression*>* alternative;
    std::list<std::pair<std::string, Carbon::Expression*>>* alternative_list;
    std::pair<Carbon::Expression*, Carbon::Statement*>* clause;
@@ -62,6 +62,7 @@ void yyerror(char* error) {
 %type <expression> expression
 %type <expression> pattern
 %type <expression> return_type
+%type <expression> paren_expression
 %type <expression> tuple
 %type <member> member
 %type <member_list> member_list
@@ -137,7 +138,7 @@ expression:
     { $$ = Carbon::MakeTypeType(yylineno); }
 | AUTO
     { $$ = Carbon::MakeAutoType(yylineno); }
-| tuple { $$ = $1; }
+| paren_expression { $$ = $1; }
 | expression EQUAL expression
     { $$ = Carbon::MakeBinOp(yylineno, Carbon::Operator::Eq, $1, $3); }
 | expression '+' expression
@@ -153,38 +154,39 @@ expression:
 | '-' expression
     { $$ = Carbon::MakeUnOp(yylineno, Carbon::Operator::Neg, $2); }
 | expression tuple
-    {
-      if ($2->tag == Carbon::ExpressionKind::Tuple) {
-        $$ = Carbon::MakeCall(yylineno, $1, $2);
-      } else {
-        auto vec =
-            new std::vector<std::pair<std::string, Carbon::Expression*>>();
-        vec->push_back(std::make_pair("", $2));
-        $$ = Carbon::MakeCall(yylineno, $1, Carbon::MakeTuple(yylineno, vec));
-      }
-    }
+    { $$ = Carbon::MakeCall(yylineno, $1, $2); }
 | FNTY tuple return_type
     { $$ = Carbon::MakeFunType(yylineno, $2, $3); }
 ;
 designator: '.' identifier { $$ = $2; }
 ;
-tuple: '(' field_list ')'
+paren_expression: '(' field_list ')'
     {
-      switch ($2->tag) {
-      case Carbon::ExpOrFieldListKind::Exp:
-        $$ = $2->u.exp;
-        break;
-      case Carbon::ExpOrFieldListKind::FieldList:
+     if ($2->fields->size() == 1 &&
+         $2->fields->front().first == "" &&
+	 !$2->has_explicit_comma) {
+	$$ = $2->fields->front().second;
+     } else {
         auto vec = new std::vector<std::pair<std::string,Carbon::Expression*>>(
-            $2->u.fields->begin(), $2->u.fields->end());
+            $2->fields->begin(), $2->fields->end());
         $$ = Carbon::MakeTuple(yylineno, vec);
-        break;
       }
     }
 ;
+tuple: '(' field_list ')'
+    {
+     auto vec = new std::vector<std::pair<std::string,Carbon::Expression*>>(
+         $2->fields->begin(), $2->fields->end());
+     $$ = Carbon::MakeTuple(yylineno, vec);
+    }
 field:
   pattern
-    { $$ = Carbon::MakeExp($1); }
+    {
+      auto fields =
+          new std::list<std::pair<std::string, Carbon::Expression*>>();
+      fields->push_back(std::make_pair("", $1));
+      $$ = Carbon::MakeFieldList(fields);
+    }
 | designator '=' pattern
     {
       auto fields =