diff --git a/lib/lrama/command.rb b/lib/lrama/command.rb
index 4530f27e..0095c1a1 100644
--- a/lib/lrama/command.rb
+++ b/lib/lrama/command.rb
@@ -61,7 +61,7 @@ def run(argv)
 
       logger = Lrama::Logger.new
       exit false unless Lrama::GrammarValidator.new(grammar, states, logger).valid?
-      Lrama::Diagnostics.new(grammar, states, logger).run(**options.diagnostic_opts)
+      Lrama::Diagnostics.new(grammar, states, logger).run(options.diagnostic)
     end
   end
 end
diff --git a/lib/lrama/diagnostics.rb b/lib/lrama/diagnostics.rb
index 1f6f9ed9..e9da398c 100644
--- a/lib/lrama/diagnostics.rb
+++ b/lib/lrama/diagnostics.rb
@@ -8,19 +8,21 @@ def initialize(grammar, states, logger)
       @logger = logger
     end
 
-    def run(conflicts_sr: false, conflicts_rr: false, parameterizing_redefined: false)
-      diagnose_conflict(conflicts_sr, conflicts_rr)
-      diagnose_parameterizing_redefined if parameterizing_redefined
+    def run(diagnostic)
+      if diagnostic
+        diagnose_conflict
+        diagnose_parameterizing_redefined
+      end
     end
 
     private
 
-    def diagnose_conflict(conflicts_sr, conflicts_rr)
-      if conflicts_sr && @states.sr_conflicts_count != 0
+    def diagnose_conflict
+      if @states.sr_conflicts_count != 0
         @logger.warn("shift/reduce conflicts: #{@states.sr_conflicts_count} found")
       end
 
-      if conflicts_rr && @states.rr_conflicts_count != 0
+      if  @states.rr_conflicts_count != 0
         @logger.warn("reduce/reduce conflicts: #{@states.rr_conflicts_count} found")
       end
     end
diff --git a/lib/lrama/option_parser.rb b/lib/lrama/option_parser.rb
index 8459e818..517693ad 100644
--- a/lib/lrama/option_parser.rb
+++ b/lib/lrama/option_parser.rb
@@ -16,7 +16,6 @@ def parse(argv)
 
       @options.trace_opts = validate_trace(@trace)
       @options.report_opts = validate_report(@report)
-      @options.diagnostic_opts = validate_diagnostic(@diagnostic)
       @options.grammar_file = argv.shift
 
       if !@options.grammar_file
@@ -82,14 +81,7 @@ def parse_by_option_parser(argv)
         o.on('-v', 'reserved, do nothing') { }
         o.separator ''
         o.separator 'Diagnostics:'
-        o.on('-W', '--warnings=CATEGORY', Array, 'report the warnings falling in category') {|v| @diagnostic = v }
-        o.separator ''
-        o.separator 'Warning categories include:'
-        o.separator '    conflicts-sr                     Shift/Reduce conflicts (enabled by default)'
-        o.separator '    conflicts-rr                     Reduce/Reduce conflicts (enabled by default)'
-        o.separator '    parameterizing-redefined         redefinition of parameterizing rule'
-        o.separator '    all                              all warnings'
-        o.separator '    none                             turn off all warnings'
+        o.on('-W', '--warnings', 'report the warnings') {|v| @options.diagnostic = true }
         o.separator ''
         o.separator 'Error Recovery:'
         o.on('-e', 'enable error recovery') {|v| @options.error_recovery = true }
@@ -151,27 +143,5 @@ def validate_trace(trace)
 
       return h
     end
-
-    DIAGNOSTICS = %w[]
-    HYPHENATED_DIAGNOSTICS = %w[conflicts-sr conflicts-rr parameterizing-redefined]
-
-    def validate_diagnostic(diagnostic)
-      h = { conflicts_sr: true, conflicts_rr: true }
-      return h if diagnostic.nil?
-      return {} if diagnostic.any? { |d| d == 'none' }
-      return { all: true } if diagnostic.any? { |d| d == 'all' }
-
-      diagnostic.each do |d|
-        if DIAGNOSTICS.include?(d)
-          h[d.to_sym] = true
-        elsif HYPHENATED_DIAGNOSTICS.include?(d)
-          h[d.gsub('-', '_').to_sym] = true
-        else
-          raise "Invalid diagnostic option \"#{d}\"."
-        end
-      end
-
-      return h
-    end
   end
 end
diff --git a/lib/lrama/options.rb b/lib/lrama/options.rb
index 9e2929ac..ccd76803 100644
--- a/lib/lrama/options.rb
+++ b/lib/lrama/options.rb
@@ -7,7 +7,7 @@ class Options
                   :report_file, :outfile,
                   :error_recovery, :grammar_file,
                   :trace_opts, :report_opts,
-                  :diagnostic_opts, :y, :debug
+                  :diagnostic, :y, :debug
 
     def initialize
       @skeleton = "bison/yacc.c"
@@ -19,7 +19,7 @@ def initialize
       @grammar_file = nil
       @trace_opts = nil
       @report_opts = nil
-      @diagnostic_opts = nil
+      @diagnostic = false
       @y = STDIN
       @debug = false
     end
diff --git a/sig/lrama/options.rbs b/sig/lrama/options.rbs
index 2fddb15d..d32dd675 100644
--- a/sig/lrama/options.rbs
+++ b/sig/lrama/options.rbs
@@ -9,7 +9,7 @@ module Lrama
     attr_accessor grammar_file: String?
     attr_accessor trace_opts: Hash[Symbol, bool]?
     attr_accessor report_opts: Hash[Symbol, bool]?
-    attr_accessor diagnostic_opts: Hash[Symbol, bool]?
+    attr_accessor diagnostic: bool
     attr_accessor y: IO
     attr_accessor debug: bool
 
diff --git a/spec/lrama/diagnostics_spec.rb b/spec/lrama/diagnostics_spec.rb
index e2d765e1..87185662 100644
--- a/spec/lrama/diagnostics_spec.rb
+++ b/spec/lrama/diagnostics_spec.rb
@@ -75,7 +75,7 @@ class : keyword_class tSTRING keyword_end %prec tPLUS
         states.compute
         logger = Lrama::Logger.new
         allow(logger).to receive(:warn)
-        Lrama::Diagnostics.new(grammar, states, logger).run(conflicts_sr: true, conflicts_rr: true)
+        Lrama::Diagnostics.new(grammar, states, logger).run(true)
         expect(logger).to have_received(:warn).with("shift/reduce conflicts: 2 found")
         expect(logger).to have_received(:warn).with("reduce/reduce conflicts: 1 found")
       end
@@ -109,7 +109,7 @@ class : keyword_class tSTRING keyword_end %prec tPLUS
         states.compute
         logger = Lrama::Logger.new
         allow(logger).to receive(:warn)
-        Lrama::Diagnostics.new(grammar, states, logger).run(parameterizing_redefined: true)
+        Lrama::Diagnostics.new(grammar, states, logger).run(true)
         expect(logger).to have_received(:warn).with("parameterizing rule redefined: foo(X)")
         expect(logger).to have_received(:warn).with("parameterizing rule redefined: foo(Y)")
       end
diff --git a/spec/lrama/option_parser_spec.rb b/spec/lrama/option_parser_spec.rb
index 270efa06..9c977e1c 100644
--- a/spec/lrama/option_parser_spec.rb
+++ b/spec/lrama/option_parser_spec.rb
@@ -61,14 +61,7 @@
               -v                               reserved, do nothing
 
           Diagnostics:
-              -W, --warnings=CATEGORY          report the warnings falling in category
-
-          Warning categories include:
-              conflicts-sr                     Shift/Reduce conflicts (enabled by default)
-              conflicts-rr                     Reduce/Reduce conflicts (enabled by default)
-              parameterizing-redefined         redefinition of parameterizing rule
-              all                              all warnings
-              none                             turn off all warnings
+              -W, --warnings                   report the warnings
 
           Error Recovery:
               -e                               enable error recovery
@@ -216,57 +209,32 @@
     end
   end
 
-  describe "@diagnostic_opts" do
+  describe "@diagnostic" do
     context "when diagnostic option is not passed" do
-      it "returns { conflicts_sr: true, conflicts_rr: true }" do
+      it "returns false" do
         option_parser = Lrama::OptionParser.new
         option_parser.send(:parse, [fixture_path("command/basic.y")])
         options = option_parser.instance_variable_get(:@options)
-        expect(options.diagnostic_opts).to eq({ conflicts_sr: true, conflicts_rr: true })
+        expect(options.diagnostic).to be false
       end
     end
 
     context "when diagnostic option is passed" do
-      context "when all is passed" do
-        it "returns { all: true }" do
-          option_parser = Lrama::OptionParser.new
-          option_parser.send(:parse, ["--warnings=all", fixture_path("command/basic.y")])
-          options = option_parser.instance_variable_get(:@options)
-          expect(options.diagnostic_opts).to eq({all: true})
-        end
-      end
-
-      context "when conflicts-sr is passed" do
-        it "returns { conflicts_sr: true, conflicts_rr: true }" do
+      context "when --warnings is passed" do
+        it "returns true" do
           option_parser = Lrama::OptionParser.new
-          option_parser.send(:parse, ["--warnings=conflicts-sr", fixture_path("command/basic.y")])
+          option_parser.send(:parse, ["--warnings", fixture_path("command/basic.y")])
           options = option_parser.instance_variable_get(:@options)
-          expect(options.diagnostic_opts).to eq({ conflicts_sr: true, conflicts_rr: true })
+          expect(options.diagnostic).to be true
         end
       end
 
-      context "when conflicts-rr is passed" do
-        it "returns { conflicts_sr: true, conflicts_rr: true }" do
+      context "when -W is passed" do
+        it "returns true" do
           option_parser = Lrama::OptionParser.new
-          option_parser.send(:parse, ["--warnings=conflicts-rr", fixture_path("command/basic.y")])
+          option_parser.send(:parse, ["-W", fixture_path("command/basic.y")])
           options = option_parser.instance_variable_get(:@options)
-          expect(options.diagnostic_opts).to eq({ conflicts_sr: true, conflicts_rr: true })
-        end
-      end
-
-      context "when none is passed" do
-        it "returns empty hash" do
-          option_parser = Lrama::OptionParser.new
-          option_parser.send(:parse, ["--warnings=none", fixture_path("command/basic.y")])
-          options = option_parser.instance_variable_get(:@options)
-          expect(options.diagnostic_opts).to eq({})
-        end
-      end
-
-      context "when invalid option is passed" do
-        it "raise error" do
-          option_parser = Lrama::OptionParser.new
-          expect { option_parser.send(:parse, ["--warnings=invalid", fixture_path("command/basic.y")]) }.to raise_error(/Invalid diagnostic option/)
+          expect(options.diagnostic).to be true
         end
       end
     end