diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
index 7415d3ce..7e5b197c 100644
--- a/CONTRIBUTING.md
+++ b/CONTRIBUTING.md
@@ -4,7 +4,7 @@ Contribute to Listen
 File an issue
 -------------
 
-If you haven't already, first see [TROUBLESHOOTING](https://github.com/guard/listen/wiki/Troubleshooting) for known issues, solutions and workarounds.
+If you haven't already, first see [TROUBLESHOOTING](https://github.com/guard/listen/blob/master/README.md#Issues-and-Troubleshooting) for known issues, solutions and workarounds.
 
 You can report bugs and feature requests to [GitHub Issues](https://github.com/guard/listen/issues).
 
@@ -16,7 +16,7 @@ Try to figure out where the issue belongs to: Is it an issue with Listen itself
 
 **It's most likely that your bug gets resolved faster if you provide as much information as possible!**
 
-The MOST useful information is debugging output from Listen (`LISTEN_GEM_DEBUGGING=1`) - see [TROUBLESHOOTING](https://github.com/guard/listen/wiki/Troubleshooting) for details.
+The MOST useful information is debugging output from Listen (`LISTEN_GEM_DEBUGGING=1`) - see [TROUBLESHOOTING](https://github.com/guard/listen/blob/master/README.md#Issues-and-Troubleshooting) for details.
 
 
 Development
diff --git a/README.md b/README.md
index 43d29e39..340b7c37 100644
--- a/README.md
+++ b/README.md
@@ -2,8 +2,6 @@
 
 The `listen` gem listens to file modifications and notifies you about the changes.
 
-:exclamation: `Listen` is currently accepting more maintainers. Please [read this](https://github.com/guard/guard/wiki/Maintainers) if you're interested in joining the team.
-
 [![Development Status](https://github.com/guard/listen/workflows/Development/badge.svg)](https://github.com/guard/listen/actions?workflow=Development)
 [![Gem Version](https://badge.fury.io/rb/listen.svg)](http://badge.fury.io/rb/listen)
 [![Code Climate](https://codeclimate.com/github/guard/listen.svg)](https://codeclimate.com/github/guard/listen)
diff --git a/lib/listen/adapter/linux.rb b/lib/listen/adapter/linux.rb
index 50653d6e..af732491 100644
--- a/lib/listen/adapter/linux.rb
+++ b/lib/listen/adapter/linux.rb
@@ -21,12 +21,12 @@ class Linux < Base
 
       private
 
-      WIKI_URL = 'https://github.com/guard/listen'\
+      README_URL = 'https://github.com/guard/listen'\
         '/blob/master/README.md#increasing-the-amount-of-inotify-watchers'
 
-      INOTIFY_LIMIT_MESSAGE = <<-EOS.gsub(/^\s*/, '')
+      INOTIFY_LIMIT_MESSAGE = <<-EOS
         FATAL: Listen error: unable to monitor directories for changes.
-        Visit #{WIKI_URL} for info on how to fix this.
+        Visit #{README_URL} for info on how to fix this.
       EOS
 
       def _configure(directory, &callback)
diff --git a/lib/listen/error.rb b/lib/listen/error.rb
new file mode 100644
index 00000000..e3c3a27c
--- /dev/null
+++ b/lib/listen/error.rb
@@ -0,0 +1,10 @@
+# frozen_string_literal: true
+
+# Besides programming error exceptions like ArgumentError,
+# all public interface exceptions should be declared here and inherit from Listen::Error.
+module Listen
+  class Error < RuntimeError
+    class NotStarted < Error; end
+    class SymlinkLoop < Error; end
+  end
+end
diff --git a/lib/listen/event/loop.rb b/lib/listen/event/loop.rb
index 9b6e2ebf..dd071f01 100644
--- a/lib/listen/event/loop.rb
+++ b/lib/listen/event/loop.rb
@@ -5,15 +5,15 @@
 require 'timeout'
 require 'listen/event/processor'
 require 'listen/thread'
+require 'listen/error'
 
 module Listen
   module Event
     class Loop
       include Listen::FSM
 
-      class Error < RuntimeError
-        class NotStarted < Error; end
-      end
+      Error = ::Listen::Error
+      NotStarted = ::Listen::Error::NotStarted # for backward compatibility
 
       start_state :pre_start
       state :pre_start
@@ -40,6 +40,7 @@ def started?
 
       MAX_STARTUP_SECONDS = 5.0
 
+      # @raises Error::NotStarted if background thread hasn't started in MAX_STARTUP_SECONDS
       def start
         # TODO: use a Fiber instead?
         return unless state == :pre_start
diff --git a/lib/listen/fsm.rb b/lib/listen/fsm.rb
index ba63fd65..154ad2b3 100644
--- a/lib/listen/fsm.rb
+++ b/lib/listen/fsm.rb
@@ -53,6 +53,9 @@ def initialize_fsm
     # if not already, waits for a state change (up to timeout seconds--`nil` means infinite)
     # returns truthy iff the transition to one of the desired state has occurred
     def wait_for_state(*wait_for_states, timeout: nil)
+      wait_for_states.each do |state|
+        state.is_a?(Symbol) or raise ArgumentError, "states must be symbols (got #{state.inspect})"
+      end
       @mutex.synchronize do
         if !wait_for_states.include?(@state)
           @state_changed.wait(@mutex, timeout)
diff --git a/lib/listen/record/symlink_detector.rb b/lib/listen/record/symlink_detector.rb
index c5d66ec0..cce87739 100644
--- a/lib/listen/record/symlink_detector.rb
+++ b/lib/listen/record/symlink_detector.rb
@@ -1,12 +1,13 @@
 # frozen_string_literal: true
 
 require 'set'
+require 'listen/error'
 
 module Listen
   # @private api
   class Record
     class SymlinkDetector
-      WIKI = 'https://github.com/guard/listen/wiki/Duplicate-directory-errors'
+      README_URL = 'https://github.com/guard/listen/blob/master/README.md'
 
       SYMLINK_LOOP_ERROR = <<-EOS
         ** ERROR: directory is already being watched! **
@@ -15,11 +16,10 @@ class SymlinkDetector
 
         is already being watched through: %s
 
-        MORE INFO: #{WIKI}
+        MORE INFO: #{README_URL}
       EOS
 
-      class Error < RuntimeError
-      end
+      Error = ::Listen::Error # for backward compatibility
 
       def initialize
         @real_dirs = Set.new
@@ -27,14 +27,14 @@ def initialize
 
       def verify_unwatched!(entry)
         real_path = entry.real_path
-        @real_dirs.add?(real_path) || _fail(entry.sys_path, real_path)
+        @real_dirs.add?(real_path) or _fail(entry.sys_path, real_path)
       end
 
       private
 
       def _fail(symlinked, real_path)
         warn(format(SYMLINK_LOOP_ERROR, symlinked, real_path))
-        raise Error, 'Failed due to looped symlinks'
+        raise ::Listen::Error::SymlinkLoop, 'Failed due to looped symlinks'
       end
     end
   end
diff --git a/listen.gemspec b/listen.gemspec
index 9ac4b647..19106787 100644
--- a/listen.gemspec
+++ b/listen.gemspec
@@ -21,8 +21,7 @@ Gem::Specification.new do |gem|
     'changelog_uri' => "#{gem.homepage}/releases",
     'documentation_uri' => "https://www.rubydoc.info/gems/listen/#{gem.version}",
     'homepage_uri' => gem.homepage,
-    'source_code_uri' => "#{gem.homepage}/tree/v#{gem.version}",
-    'wiki_uri' => "#{gem.homepage}/wiki"
+    'source_code_uri' => "#{gem.homepage}/tree/v#{gem.version}"
   }
 
   gem.files = `git ls-files -z`.split("\x0").select do |f|
diff --git a/spec/lib/listen/event/loop_spec.rb b/spec/lib/listen/event/loop_spec.rb
index 749d4351..1d2aed7a 100644
--- a/spec/lib/listen/event/loop_spec.rb
+++ b/spec/lib/listen/event/loop_spec.rb
@@ -45,26 +45,40 @@
   end
 
   describe '#start' do
-    before do
+    it 'is started' do
+      expect(processor).to receive(:loop_for).with(1.234)
       expect(Thread).to receive(:new) do |&block|
         block.call
         thread
       end
-
-      expect(processor).to receive(:loop_for).with(1.234)
-
       subject.start
-    end
-
-    it 'is started' do
       expect(subject).to be_started
     end
 
     context 'when start is called again' do
       it 'returns silently' do
+        expect(processor).to receive(:loop_for).with(1.234)
+        expect(Thread).to receive(:new) do |&block|
+          block.call
+          thread
+        end
+        subject.start
         expect { subject.start }.to_not raise_exception
       end
     end
+
+    context 'when state change to :started takes longer than 5 seconds' do
+      before do
+        expect(Thread).to receive(:new) { thread }
+        expect_any_instance_of(::ConditionVariable).to receive(:wait) { } # return immediately
+      end
+
+      it 'raises Error::NotStarted' do
+        expect do
+          subject.start
+        end.to raise_exception(::Listen::Error::NotStarted, "thread didn't start in 5.0 seconds (in state: :starting)")
+      end
+    end
   end
 
   context 'when set up / started' do
diff --git a/spec/lib/listen/fsm_spec.rb b/spec/lib/listen/fsm_spec.rb
index a4395f28..359afa75 100644
--- a/spec/lib/listen/fsm_spec.rb
+++ b/spec/lib/listen/fsm_spec.rb
@@ -60,6 +60,44 @@ def initialize
       expect { subject.transition(:started) }.to raise_exception(NoMethodError, /private.*transition/)
       expect { subject.transition!(:started) }.to raise_exception(NoMethodError, /private.*transition!/)
     end
+
+    describe '#wait_for_state' do
+      it 'returns truthy immediately if already in the desired state' do
+        expect(subject.instance_variable_get(:@state_changed)).to_not receive(:wait)
+        result = subject.wait_for_state(:initial)
+        expect(result).to be_truthy
+      end
+
+      it 'waits for the next state change and returns truthy if then in the desired state' do
+        expect(subject.instance_variable_get(:@state_changed)).to receive(:wait).with(anything, anything) do
+          subject.instance_variable_set(:@state, :started)
+        end
+        result = subject.wait_for_state(:started)
+        expect(result).to be_truthy
+      end
+
+      it 'waits for the next state change and returns falsey if then not the desired state' do
+        expect(subject.instance_variable_get(:@state_changed)).to receive(:wait).with(anything, anything)
+        result = subject.wait_for_state(:started)
+        expect(result).to be_falsey
+      end
+
+      it 'passes the timeout: down to wait, if given' do
+        expect(subject.instance_variable_get(:@state_changed)).to receive(:wait).with(anything, 5.0)
+        subject.wait_for_state(:started, timeout: 5.0)
+      end
+
+      it 'passes nil (infinite) timeout: down to wait, if none given' do
+        expect(subject.instance_variable_get(:@state_changed)).to receive(:wait).with(anything, nil)
+        subject.wait_for_state(:started)
+      end
+
+      it 'enforces precondition that states must be symbols' do
+        expect do
+          subject.wait_for_state(:started, 'stopped')
+        end.to raise_exception(ArgumentError, /states must be symbols .*got "stopped"/)
+      end
+    end
   end
 
   context 'FSM with no start state' do