diff --git a/CHANGELOG.md b/CHANGELOG.md
index be01d2e..ba84cde 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,5 +1,6 @@
 ## HEAD (unreleased)
 
+- Support "endless" oneline method definitions for Ruby 3+ (https://github.com/zombocom/dead_end/pull/80)
 - Reduce timeout to 1 second (https://github.com/zombocom/dead_end/pull/79)
 - Logically consecutive lines (such as chained methods are now joined) (https://github.com/zombocom/dead_end/pull/78)
 - Output improvement for cases where the only line is an single `end` (https://github.com/zombocom/dead_end/pull/78)
diff --git a/lib/dead_end/code_line.rb b/lib/dead_end/code_line.rb
index ebf8a49..8718fdb 100644
--- a/lib/dead_end/code_line.rb
+++ b/lib/dead_end/code_line.rb
@@ -60,6 +60,8 @@ def initialize(line:, index:, lex:)
         end_count += 1 if lex.is_end?
       end
 
+      kw_count -= oneliner_method_count
+
       @is_kw = (kw_count - end_count) > 0
       @is_end = (end_count - kw_count) > 0
     end
@@ -195,5 +197,37 @@ def trailing_slash?
 
       last.token == TRAILING_SLASH
     end
+
+    # Endless method detection
+    #
+    # From https://github.com/ruby/irb/commit/826ae909c9c93a2ddca6f9cfcd9c94dbf53d44ab
+    # Detecting a "oneliner" seems to need a state machine.
+    # This can be done by looking mostly at the "state" (last value):
+    #
+    #   ENDFN -> BEG (token = '=' ) -> END
+    #
+    private def oneliner_method_count
+      oneliner_count = 0
+      in_oneliner_def = nil
+
+      @lex.each do |lex|
+        if in_oneliner_def.nil?
+          in_oneliner_def = :ENDFN if lex.state.allbits?(Ripper::EXPR_ENDFN)
+        elsif lex.state.allbits?(Ripper::EXPR_ENDFN)
+          # Continue
+        elsif lex.state.allbits?(Ripper::EXPR_BEG)
+          in_oneliner_def = :BODY if lex.token == "="
+        elsif lex.state.allbits?(Ripper::EXPR_END)
+          # We found an endless method, count it
+          oneliner_count += 1 if in_oneliner_def == :BODY
+
+          in_oneliner_def = nil
+        else
+          in_oneliner_def = nil
+        end
+      end
+
+      oneliner_count
+    end
   end
 end
diff --git a/spec/unit/code_line_spec.rb b/spec/unit/code_line_spec.rb
index 29324cf..1eb1a86 100644
--- a/spec/unit/code_line_spec.rb
+++ b/spec/unit/code_line_spec.rb
@@ -4,6 +4,17 @@
 
 module DeadEnd
   RSpec.describe CodeLine do
+    it "supports endless method definitions" do
+      skip("Unsupported ruby version") unless Gem::Version.new(RUBY_VERSION) >= Gem::Version.new("3")
+
+      line = CodeLine.from_source(<<~'EOM').first
+        def square(x) = x * x
+      EOM
+
+      expect(line.is_kw?).to be_falsey
+      expect(line.is_end?).to be_falsey
+    end
+
     it "retains original line value, after being marked invisible" do
       line = CodeLine.from_source(<<~'EOM').first
         puts "lol"