diff --git a/ir/emit.cc b/ir/emit.cc
index a0592cd2..f66b46d1 100644
--- a/ir/emit.cc
+++ b/ir/emit.cc
@@ -576,6 +576,12 @@ void HandleParseTreeNodeFunctionTypeParameters(ParseNodeIndex index,
           .returns    = 1});
 }
 
+void HandleParseTreeNodeEmptyParenthesis(ParseNodeIndex index,
+                                         EmitContext& context) {
+  jasmin::Value v = type::Bottom;
+  context.Push(std::span(&v, 1), type::Type_);
+}
+
 void HandleParseTreeNodeEnumLiteralStart(ParseNodeIndex, EmitContext&) {
   NTH_UNIMPLEMENTED();
 }
diff --git a/ir/function.cc b/ir/function.cc
index 17a601e9..11c404a0 100644
--- a/ir/function.cc
+++ b/ir/function.cc
@@ -125,4 +125,18 @@ void InvokeForeignFunction::consume(std::span<jasmin::Value> input,
   }
 }
 
+type::Type ConstructFunctionType::consume(std::span<jasmin::Value, 2> inputs) {
+  auto parameter   = inputs[0].as<type::Type>();
+  auto return_type = inputs[1].as<type::Type>();
+  std::vector<type::Type> returns;
+  if (return_type != type::Bottom) { returns.push_back(return_type); }
+  if (parameter.kind() == type::Type::Kind::Parameters) {
+    return type::Function(parameter.AsParameters(), std::move(returns));
+  } else {
+    return type::Function(
+        type::Parameters({{.name = Identifier("").value(), .type = parameter}}),
+        std::move(returns));
+  }
+}
+
 }  // namespace ic
diff --git a/ir/function.h b/ir/function.h
index 3c5b9872..045eccd1 100644
--- a/ir/function.h
+++ b/ir/function.h
@@ -102,17 +102,7 @@ struct ConstructParametersType : jasmin::Instruction<ConstructParametersType> {
 struct ConstructFunctionType : jasmin::Instruction<ConstructFunctionType> {
   static std::string_view name() { return "construct-function-type"; }
 
-  static type::Type consume(std::span<jasmin::Value, 2> inputs) {
-    auto parameter   = inputs[0].as<type::Type>();
-    auto return_type = inputs[1].as<type::Type>();
-    if (parameter.kind() == type::Type::Kind::Parameters) {
-      return type::Function(parameter.AsParameters(), std::vector{return_type});
-    } else {
-      return type::Function(type::Parameters({{.name = Identifier("").value(),
-                                               .type = parameter}}),
-                            std::vector{return_type});
-    }
-  }
+  static type::Type consume(std::span<jasmin::Value, 2> inputs);
 };
 
 struct ConstructOpaqueType : jasmin::Instruction<ConstructOpaqueType> {
diff --git a/ir/ir.cc b/ir/ir.cc
index 62bedea5..42c09b55 100644
--- a/ir/ir.cc
+++ b/ir/ir.cc
@@ -470,7 +470,9 @@ void HandleParseTreeNodeExpressionPrecedenceGroup(
         });
       }
       NTH_REQUIRE(context.type_stack().group_count() >= 2);
-      type::Type return_type = context.type_stack().top()[0].type();
+      std::span return_types = context.type_stack().top();
+      std::optional<type::Type> return_type;
+      if (not return_types.empty()) { return_type = return_types[0].type(); }
       context.type_stack().pop();
       type::Type parameters_type = context.type_stack().top()[0].type();
       auto iter                  = context.Children(index).begin();
@@ -485,7 +487,8 @@ void HandleParseTreeNodeExpressionPrecedenceGroup(
         });
       }
 
-      if (return_type != type::Type_) {
+      if (return_type and return_type != type::Type_) {
+        NTH_LOG("{}") <<= {return_type};
         auto iter = context.Children(index).begin();
         diag.Consume({
             diag::Header(diag::MessageKind::Error),
@@ -820,6 +823,12 @@ void HandleParseTreeNodeCallExpression(ParseNodeIndex index, IrContext& context,
   }
 }
 
+void HandleParseTreeNodeEmptyParenthesis(ParseNodeIndex index,
+                                         IrContext& context,
+                                         diag::DiagnosticConsumer& diag) {
+  context.type_stack().push({});
+}
+
 void HandleParseTreeNodeDeclaredIdentifier(ParseNodeIndex index,
                                            IrContext& context,
                                            diag::DiagnosticConsumer& diag) {
diff --git a/parse/node.xmacro.h b/parse/node.xmacro.h
index 80ec5b5f..fe508bf4 100644
--- a/parse/node.xmacro.h
+++ b/parse/node.xmacro.h
@@ -83,6 +83,7 @@ IC_XMACRO_PARSE_NODE_EXPRESSION(Identifier)
 IC_XMACRO_PARSE_NODE_EXPRESSION(ExpressionPrecedenceGroup)
 IC_XMACRO_PARSE_NODE_EXPRESSION(MemberExpression)
 IC_XMACRO_PARSE_NODE_EXPRESSION(EnumLiteral)
+IC_XMACRO_PARSE_NODE_EXPRESSION(EmptyParenthesis)
 
 IC_XMACRO_PARSE_NODE_EXPRESSION(Scope)
 
diff --git a/parse/parser.cc b/parse/parser.cc
index e6550fd6..cd0dcfa2 100644
--- a/parse/parser.cc
+++ b/parse/parser.cc
@@ -509,6 +509,13 @@ void Parser::HandleParenthesizedExpression(ParseTree& tree) {
   if (current_token().kind() == Token::Kind::LeftParen) {
     ++iterator_;
     IgnoreAnyNewlines();
+    if (current_token().kind() == Token::Kind::RightParen) {
+      auto state = pop_state();
+      tree.append(ParseNode::Kind::EmptyParenthesis, state.token,
+                  state.subtree_start);
+      ++iterator_;
+      return;
+    }
     ExpandState(Expression(tree), State::Kind::ClosingParenthesis);
   } else {
     NTH_UNIMPLEMENTED();
diff --git a/toolchain/stdlib/compat/c/errno.ic b/toolchain/stdlib/compat/c/errno.ic
index 395ad637..2987d31f 100644
--- a/toolchain/stdlib/compat/c/errno.ic
+++ b/toolchain/stdlib/compat/c/errno.ic
@@ -3,5 +3,5 @@
 let c ::= import "std.compat.c.types"
 
 let errno    ::= builtin.foreign("errno", *c.int)
-// let perror   ::= builtin.foreign("perror", [*]char -> ())
+let perror   ::= builtin.foreign("perror", [*]char -> ())
 let strerror ::= builtin.foreign("strerror", c.int -> [*]char)
diff --git a/toolchain/stdlib/compat/c/stdio.template.ic b/toolchain/stdlib/compat/c/stdio.template.ic
index fae48e69..7cc92aff 100644
--- a/toolchain/stdlib/compat/c/stdio.template.ic
+++ b/toolchain/stdlib/compat/c/stdio.template.ic
@@ -25,11 +25,11 @@ let fopen    ::= builtin.foreign("fopen", ([*]char, [*]char) -> *FILE)
 let freopen  ::= builtin.foreign("freopen", ([*]char, [*]char, *FILE) -> *FILE)
 let fclose   ::= builtin.foreign("fclose", *FILE -> c.int)
 let fflush   ::= builtin.foreign("fflush", *FILE -> c.int)
-// let setbuf   ::= builtin.foreign("setbuf", (*FILE, [*]char) -> ())
-// let setvbuf  ::= builtin.foreign("setvbuf", (*FILE, [*]char, c.int, c.size_t) -> c.int)
+let setbuf   ::= builtin.foreign("setbuf", (*FILE, [*]char) -> ())
+let setvbuf  ::= builtin.foreign("setvbuf", (*FILE, [*]char, c.int, size_t) -> c.int)
 
-// let fread    ::= builtin.foreign("fread", ([*]byte, c.size_t, c.size_t, *FILE) -> c.size_t)
-// let fwrite   ::= builtin.foreign("fwrite", ([*]byte, c.size_t, c.size_t, *FILE) -> c.size_t)
+let fread    ::= builtin.foreign("fread", ([*]byte, size_t, size_t, *FILE) -> size_t)
+let fwrite   ::= builtin.foreign("fwrite", ([*]byte, size_t, size_t, *FILE) -> size_t)
 
 let fgetc    ::= builtin.foreign("fgetc", *FILE -> c.int)
 let getc     ::= builtin.foreign("getc", *FILE -> c.int)
@@ -48,9 +48,9 @@ let fseek    ::= builtin.foreign("fseek", (*FILE, c.long, c.int) -> c.int)
 let fsetpos  ::= builtin.foreign("fsetpos", (*FILE, *fpos_t) -> c.int)
 let rewind   ::= builtin.foreign("rewind", *FILE -> c.int)
 
-// let clearerr ::= builtin.foreign("clearerr", *FILE -> ())
+let clearerr ::= builtin.foreign("clearerr", *FILE -> ())
 let feof     ::= builtin.foreign("feof", *FILE -> c.int)
-// let ferror   ::= builtin.foreign("ferror", *FILE -> ())
+let ferror   ::= builtin.foreign("ferror", *FILE -> ())
 let perror   ::= builtin.foreign("perror", [*]char -> c.int)
 
 let remove   ::= builtin.foreign("remove", [*]char -> c.int)