diff --git a/.rdoc_options b/.rdoc_options
index 2826c2d5e8..910bdbaba5 100644
--- a/.rdoc_options
+++ b/.rdoc_options
@@ -6,3 +6,4 @@ exclude:
 op_dir: _site # for GitHub Pages and should match the config of RDoc task in Rakefile
 title: rdoc Documentation
 main_page: README.rdoc
+warn_missing_rdoc_ref: true
diff --git a/lib/rdoc/markup/to_html_crossref.rb b/lib/rdoc/markup/to_html_crossref.rb
index 9b5de62fd6..172518c7f9 100644
--- a/lib/rdoc/markup/to_html_crossref.rb
+++ b/lib/rdoc/markup/to_html_crossref.rb
@@ -58,7 +58,7 @@ def init_link_notation_regexp_handlings
   # Creates a link to the reference +name+ if the name exists.  If +text+ is
   # given it is used as the link text, otherwise +name+ is used.
 
-  def cross_reference name, text = nil, code = true
+  def cross_reference name, text = nil, code = true, rdoc_ref: false
     lookup = name
 
     name = name[1..-1] unless @show_hash if name[0, 1] == '#'
@@ -70,7 +70,7 @@ def cross_reference name, text = nil, code = true
       text ||= name
     end
 
-    link lookup, text, code
+    link lookup, text, code, rdoc_ref: rdoc_ref
   end
 
   ##
@@ -92,7 +92,7 @@ def handle_regexp_CROSSREF(target)
       return name if name =~ /\A[a-z]*\z/
     end
 
-    cross_reference name
+    cross_reference name, rdoc_ref: false
   end
 
   ##
@@ -100,9 +100,14 @@ def handle_regexp_CROSSREF(target)
   # handle other schemes.
 
   def handle_regexp_HYPERLINK target
-    return cross_reference $' if target.text =~ /\Ardoc-ref:/
+    url = target.text
 
-    super
+    case url
+    when /\Ardoc-ref:/
+      cross_reference $', rdoc_ref: true
+    else
+      super
+    end
   end
 
   ##
@@ -117,8 +122,8 @@ def handle_regexp_RDOCLINK target
     url = target.text
 
     case url
-    when /\Ardoc-ref:/ then
-      cross_reference $'
+    when /\Ardoc-ref:/
+      cross_reference $', rdoc_ref: true
     else
       super
     end
@@ -129,16 +134,18 @@ def handle_regexp_RDOCLINK target
   # RDoc::Markup::ToHtml to handle other schemes.
 
   def gen_url url, text
-    return super unless url =~ /\Ardoc-ref:/
-
-    name = $'
-    cross_reference name, text, name == text
+    if url =~ /\Ardoc-ref:/
+      name = $'
+      cross_reference name, text, name == text, rdoc_ref: true
+    else
+      super
+    end
   end
 
   ##
   # Creates an HTML link to +name+ with the given +text+.
 
-  def link name, text, code = true
+  def link name, text, code = true, rdoc_ref: false
     if !(name.end_with?('+@', '-@')) and name =~ /(.*[^#:])?@/
       name = $1
       label = $'
@@ -148,6 +155,9 @@ def link name, text, code = true
 
     case ref
     when String then
+      if rdoc_ref && @options.warn_missing_rdoc_ref
+        puts "#{@from_path}: `rdoc-ref:#{name}` can't be resolved for `#{text}`"
+      end
       ref
     else
       path = ref ? ref.as_href(@from_path) : +""
diff --git a/lib/rdoc/options.rb b/lib/rdoc/options.rb
index a607a76d56..f35467e312 100644
--- a/lib/rdoc/options.rb
+++ b/lib/rdoc/options.rb
@@ -325,6 +325,12 @@ class RDoc::Options
 
   attr_accessor :verbosity
 
+  ##
+  # Warn if rdoc-ref links can't be resolved
+  # Default is +false+
+
+  attr_accessor :warn_missing_rdoc_ref
+
   ##
   # URL of web cvs frontend
 
@@ -393,6 +399,7 @@ def init_ivars # :nodoc:
     @update_output_dir = true
     @verbosity = 1
     @visibility = :protected
+    @warn_missing_rdoc_ref = false
     @webcvs = nil
     @write_options = false
     @encoding = Encoding::UTF_8
@@ -457,6 +464,8 @@ def override map # :nodoc:
     @visibility     = map['visibility']     if map.has_key?('visibility')
     @webcvs         = map['webcvs']         if map.has_key?('webcvs')
 
+    @warn_missing_rdoc_ref = map['warn_missing_rdoc_ref'] if map.has_key?('warn_missing_rdoc_ref')
+
     if map.has_key?('rdoc_include')
       @rdoc_include = sanitize_path map['rdoc_include']
     end
@@ -1104,6 +1113,13 @@ def parse argv
 
       opt.separator nil
 
+      opt.on("--warn-missing-rdoc-ref",
+             "Warn if rdoc-ref links can't be resolved") do |value|
+        @warn_missing_rdoc_ref = value
+      end
+
+      opt.separator nil
+
       opt.on("--[no-]ignore-invalid",
              "Ignore invalid options and continue",
              "(default true).") do |value|
diff --git a/test/rdoc/test_rdoc_markup_to_html_crossref.rb b/test/rdoc/test_rdoc_markup_to_html_crossref.rb
index dc4488195a..08acbc4688 100644
--- a/test/rdoc/test_rdoc_markup_to_html_crossref.rb
+++ b/test/rdoc/test_rdoc_markup_to_html_crossref.rb
@@ -1,7 +1,7 @@
 # frozen_string_literal: true
 require_relative 'xref_test_case'
 
-class TestRDocMarkupToHtmlCrossref < XrefTestCase
+class RDocMarkupToHtmlCrossrefTest < XrefTestCase
 
   def setup
     super
@@ -67,6 +67,16 @@ def test_convert_RDOCLINK_rdoc_ref
     assert_equal para("<a href=\"C1.html\"><code>C1</code></a>"), result
   end
 
+  def test_convert_RDOCLINK_rdoc_ref_not_found
+    result = nil
+    stdout, _ = capture_output do
+      result = @to.convert 'rdoc-ref:FOO'
+    end
+
+    assert_equal para("FOO"), result
+    assert_include stdout, "index.html: `rdoc-ref:FOO` can't be resolved for `FOO`"
+  end
+
   def test_convert_RDOCLINK_rdoc_ref_method
     result = @to.convert 'rdoc-ref:C1#m'
 
@@ -153,6 +163,14 @@ def test_gen_url
                  @to.gen_url('http://example', 'HTTP example')
   end
 
+  def test_gen_url_rdoc_ref_not_found
+    stdout, _ = capture_output do
+      @to.gen_url 'rdoc-ref:FOO', 'FOO'
+    end
+
+    assert_include stdout, "index.html: `rdoc-ref:FOO` can't be resolved for `FOO`"
+  end
+
   def test_handle_regexp_CROSSREF
     assert_equal "<a href=\"C2/C3.html\"><code>C2::C3</code></a>", REGEXP_HANDLING('C2::C3')
   end