diff --git a/src/server.rb b/src/server.rb
index d5876cf7..7c281ff0 100644
--- a/src/server.rb
+++ b/src/server.rb
@@ -136,16 +136,16 @@
           end
 
         if response
-          socket.write(JSON.fast_generate(response.force_encoding("UTF-8")))
+          socket.write(JSON.generate(response.force_encoding("UTF-8")))
         else
           socket.write("{ \"error\": true }")
         end
       rescue SyntaxTree::Parser::ParseError => error
         loc = { start: { line: error.lineno, column: error.column } }
-        socket.write(JSON.fast_generate(error: error.message, loc: loc))
+        socket.write(JSON.generate(error: error.message, loc: loc))
       rescue StandardError => error
         begin
-          socket.write(JSON.fast_generate(error: error.message))
+          socket.write(JSON.generate(error: error.message))
         rescue Errno::EPIPE
           # Do nothing, the pipe has been closed by the parent process so we
           # don't actually care about writing to it anymore.
@@ -163,5 +163,5 @@
     end
   end
 
-File.write(connection_filepath, JSON.fast_generate(connection_information))
+File.write(connection_filepath, JSON.generate(connection_information))
 listener.join
diff --git a/test/js/rbs/combination.txt b/test/js/rbs/combination.txt
index 2761e7a7..5a9ae9e2 100644
--- a/test/js/rbs/combination.txt
+++ b/test/js/rbs/combination.txt
@@ -1,5 +1,5 @@
-untyped | void | nil
-untyped & void & nil
-untyped | void & nil
-untyped & void | nil
-untyped & (void | nil)
+untyped | bool | nil
+untyped & bool & nil
+untyped | bool & nil
+untyped & bool | nil
+untyped & (bool | nil)
diff --git a/test/js/rbs/optional.txt b/test/js/rbs/optional.txt
index e7842ee6..65fc51b6 100644
--- a/test/js/rbs/optional.txt
+++ b/test/js/rbs/optional.txt
@@ -1,5 +1,5 @@
 untyped?
 ^-> untyped?
-untyped | void?
+untyped | bool?
 :foo??
 :foo!?
diff --git a/test/js/rbs/plain.txt b/test/js/rbs/plain.txt
index 99ab75f5..bc45ed4c 100644
--- a/test/js/rbs/plain.txt
+++ b/test/js/rbs/plain.txt
@@ -1,4 +1,3 @@
-void
 untyped
 bool
 true
@@ -6,6 +5,3 @@ false
 nil
 top
 bot
-self
-instance
-class
diff --git a/test/js/rbs/proc.txt b/test/js/rbs/proc.txt
index 4d77333b..f7eaeac8 100644
--- a/test/js/rbs/proc.txt
+++ b/test/js/rbs/proc.txt
@@ -1,9 +1,9 @@
 ^-> void
 ^(untyped) -> void
-^(untyped, void) -> void
-^(untyped x, void _y) -> void
-^(untyped x, ?void, ?nil y) -> void
-^(untyped x, ?void, ?nil y, *untyped a) -> void
+^(untyped, bool) -> void
+^(untyped x, bool _y) -> void
+^(untyped x, ?bool, ?nil y) -> void
+^(untyped x, ?bool, ?nil y, *untyped a) -> void
 ^(untyped x, *untyped a, nil z) -> void
 ^(foo: untyped, _bar: nil bar) -> void
 ^(?_bar: nil, **untyped rest) -> void
diff --git a/test/js/rbs/rbs.test.js b/test/js/rbs/rbs.test.js
index 3e6addac..c45974af 100644
--- a/test/js/rbs/rbs.test.js
+++ b/test/js/rbs/rbs.test.js
@@ -283,7 +283,21 @@ describe("rbs", () => {
     });
   });
 
-  describeCases("plain", (source) => `T: ${source}`);
+  describe("plain", () => {
+    testCases("plain", (source) => `T: ${source}`);
+
+    ["void", "self", "instance", "class"].forEach((source) => {
+      test(source, () => {
+        const content = rbs(`
+        class T
+          def t: -> ${source}
+        end
+      `);
+
+        return expect(content).toMatchFormat();
+      });
+    });
+  });
 
   describe("proc", () => {
     testCases("proc", (source) => `T: ${source}`);
diff --git a/test/js/rbs/tuple.txt b/test/js/rbs/tuple.txt
index 7dd425e4..2f82dfa4 100644
--- a/test/js/rbs/tuple.txt
+++ b/test/js/rbs/tuple.txt
@@ -1,3 +1,3 @@
 [ ]
-[untyped, nil, void]
+[untyped, nil, bool]
 [untyped]