diff --git a/lib/reline.rb b/lib/reline.rb
index ddb0224180..4ba74d2cb2 100644
--- a/lib/reline.rb
+++ b/lib/reline.rb
@@ -412,7 +412,7 @@ module Reline
     end
 
     private def may_req_ambiguous_char_width
-      @ambiguous_width = 2 if io_gate.dumb? || !STDIN.tty? || !STDOUT.tty?
+      @ambiguous_width = 1 if io_gate.dumb? || !STDIN.tty? || !STDOUT.tty?
       return if defined? @ambiguous_width
       io_gate.move_cursor_column(0)
       begin
@@ -421,7 +421,7 @@ module Reline
         # LANG=C
         @ambiguous_width = 1
       else
-        @ambiguous_width = io_gate.cursor_pos.x
+        @ambiguous_width = io_gate.cursor_pos.x == 2 ? 2 : 1
       end
       io_gate.move_cursor_column(0)
       io_gate.erase_after_cursor
diff --git a/lib/reline/io/ansi.rb b/lib/reline/io/ansi.rb
index a730a953f7..82d2ee2371 100644
--- a/lib/reline/io/ansi.rb
+++ b/lib/reline/io/ansi.rb
@@ -245,39 +245,30 @@ class Reline::ANSI < Reline::IO
     self
   end
 
-  def cursor_pos
-    if both_tty?
-      res = +''
-      m = nil
-      @input.raw do |stdin|
-        @output << "\e[6n"
-        @output.flush
-        loop do
-          c = stdin.getc
-          next if c.nil?
-          res << c
-          m = res.match(/\e\[(?<row>\d+);(?<column>\d+)R/)
-          break if m
-        end
-        (m.pre_match + m.post_match).chars.reverse_each do |ch|
-          stdin.ungetc ch
+  private def cursor_pos_internal(timeout:)
+    match = nil
+    @input.raw do |stdin|
+      @output << "\e[6n"
+      @output.flush
+      timeout_at = Time.now + timeout
+      buf = +''
+      while (wait = timeout_at - Time.now) > 0 && stdin.wait_readable(wait)
+        buf << stdin.readpartial(1024)
+        if (match = buf.match(/\e\[(?<row>\d+);(?<column>\d+)R/))
+          buf = match.pre_match + match.post_match
+          break
         end
       end
-      column = m[:column].to_i - 1
-      row = m[:row].to_i - 1
-    else
-      begin
-        buf = @output.pread(@output.pos, 0)
-        row = buf.count("\n")
-        column = buf.rindex("\n") ? (buf.size - buf.rindex("\n")) - 1 : 0
-      rescue Errno::ESPIPE, IOError
-        # Just returns column 1 for ambiguous width because this I/O is not
-        # tty and can't seek.
-        row = 0
-        column = 1
+      buf.chars.reverse_each do |ch|
+        stdin.ungetc ch
       end
     end
-    Reline::CursorPos.new(column, row)
+    [match[:column].to_i - 1, match[:row].to_i - 1] if match
+  end
+
+  def cursor_pos
+    col, row = cursor_pos_internal(timeout: 0.5) if both_tty?
+    Reline::CursorPos.new(col || 0, row || 0)
   end
 
   def both_tty?
diff --git a/lib/reline/io/dumb.rb b/lib/reline/io/dumb.rb
index 6ed69ffdfa..6a10af4fef 100644
--- a/lib/reline/io/dumb.rb
+++ b/lib/reline/io/dumb.rb
@@ -60,7 +60,7 @@ class Reline::Dumb < Reline::IO
   end
 
   def cursor_pos
-    Reline::CursorPos.new(1, 1)
+    Reline::CursorPos.new(0, 0)
   end
 
   def hide_cursor
diff --git a/test/reline/test_reline.rb b/test/reline/test_reline.rb
index 515805467d..22437eef9b 100644
--- a/test/reline/test_reline.rb
+++ b/test/reline/test_reline.rb
@@ -1,6 +1,10 @@
 require_relative 'helper'
 require 'reline'
 require 'stringio'
+begin
+  require "pty"
+rescue LoadError # some platforms don't support PTY
+end
 
 class Reline::Test < Reline::TestCase
   class DummyCallbackObject
@@ -432,6 +436,37 @@ class Reline::Test < Reline::TestCase
     /mswin|mingw/.match?(RUBY_PLATFORM)
   end
 
+  def test_tty_amibuous_width
+    omit unless defined?(PTY)
+    ruby_file = Tempfile.create('rubyfile')
+    ruby_file.write(<<~RUBY)
+      require 'reline'
+      Thread.new { sleep 2; puts 'timeout'; exit }
+      p [Reline.ambiguous_width, gets.chomp]
+    RUBY
+    ruby_file.close
+    lib = File.expand_path('../../lib', __dir__)
+    cmd = [{ 'TERM' => 'xterm' }, 'ruby', '-I', lib, ruby_file.to_path]
+
+    # Calculate ambiguous width from cursor position
+    [1, 2].each do |ambiguous_width|
+      PTY.spawn(*cmd) do |r, w, pid|
+        loop { break if r.readpartial(1024).include?("\e[6n") }
+        w.puts "hello\e[10;#{ambiguous_width + 1}Rworld"
+        assert_include(r.gets, [ambiguous_width, 'helloworld'].inspect)
+        Process.waitpid pid
+      end
+    end
+
+    # Ambiguous width = 1 when cursor pos timed out
+    PTY.spawn(*cmd) do |r, w, pid|
+      loop { break if r.readpartial(1024).include?("\e[6n") }
+      w.puts "hello\e[10;2Sworld"
+      assert_include(r.gets, [1, "hello\e[10;2Sworld"].inspect)
+      Process.waitpid pid
+    end
+  end
+
   def get_reline_encoding
     if encoding = Reline.core.encoding
       encoding
diff --git a/test/reline/test_unicode.rb b/test/reline/test_unicode.rb
index 688d25e238..6aea8df9bb 100644
--- a/test/reline/test_unicode.rb
+++ b/test/reline/test_unicode.rb
@@ -15,7 +15,7 @@ class Reline::Unicode::Test < Reline::TestCase
   end
 
   def test_ambiguous_width
-    assert_equal 2, Reline::Unicode.calculate_width('√', true)
+    assert_equal 1, Reline::Unicode.calculate_width('√', true)
   end
 
   def test_csi_regexp