diff --git a/lib/debug/console.rb b/lib/debug/console.rb
index b228086d9..e0a9835a4 100644
--- a/lib/debug/console.rb
+++ b/lib/debug/console.rb
@@ -10,11 +10,10 @@ class Console
       include Color
 
       def parse_input buff, commands
-        c, rest = get_command buff
         case
-        when commands.keys.include?(c)
+        when Session.command?(buff, commands: commands)
           :command
-        when !rest && /\A\s*[a-z]*\z/ =~ c
+        when buff.lines.size <= 1 && buff.match?(/\A\s*[a-z]*\s*\z/)
           nil
         else
           :ruby
@@ -29,16 +28,14 @@ def readline_setup prompt
         prev_output_modifier_proc = Reline.output_modifier_proc
         prev_prompt_proc = Reline.prompt_proc
 
-        # prompt state
-        state = nil # :command, :ruby, nil (unknown)
-
-        Reline.prompt_proc = -> args, *kw do
-          case state = parse_input(args.first, commands)
+        Reline.prompt_proc = -> lines, *kw do
+          input = lines.map { |line| "#{line}\n" }.join
+          case parse_input(input, commands)
           when nil, :command
             [prompt]
           when :ruby
             [prompt.sub('rdbg'){colorize('ruby', [:RED])}]
-          end * args.size
+          end * lines.size
         end
 
         Reline.completion_proc = -> given do
@@ -58,10 +55,10 @@ def readline_setup prompt
         end
 
         Reline.output_modifier_proc = -> buff, **kw do
-          c, rest = get_command buff
-
-          case state
+          case parse_input(buff, commands)
           when :command
+            # buff is single line if it's command
+            /\A(?<leading_spaces>\s*)(?<c>[^\s]+)(?<rest>.*)/ =~ buff.chomp
             cmd = colorize(c, [:CYAN, :UNDERLINE])
 
             if commands[c] == c
@@ -71,7 +68,7 @@ def readline_setup prompt
             end
 
             rest = rest ? colorize_code(rest) : ''
-            cmd + rest + rprompt
+            [leading_spaces, cmd, rest, rprompt].join
           when nil
             buff
           when :ruby
@@ -87,15 +84,6 @@ def readline_setup prompt
         Reline.prompt_proc = prev_prompt_proc
       end
 
-      private def get_command line
-        case line.chomp
-        when /\A(\s*[a-z]+)(\s.*)?\z$/
-          return $1.strip, $2
-        else
-          line.strip
-        end
-      end
-
       def readline prompt
         readline_setup prompt do
           Reline.readmultiline(prompt, true){ true }
diff --git a/lib/debug/session.rb b/lib/debug/session.rb
index 05dc7f508..cfdc155aa 100644
--- a/lib/debug/session.rb
+++ b/lib/debug/session.rb
@@ -1142,6 +1142,18 @@ def register_default_command
       end
     end
 
+    ASSIGN_OPERATORS_REGEXP = Regexp.union(%w[= += -= *= /= %= **= &= |= &&= ||= ^= <<= >>=])
+
+    def self.command?(line, commands:)
+      return false if line.lines.size != 1
+
+      command, arg = line.lstrip.split(/\s+/, 2)
+      return false unless commands.has_key? command
+
+      # assignment-like expression should be treated as ruby code, not as commands.
+      !arg || !arg.start_with?(ASSIGN_OPERATORS_REGEXP) || arg.start_with?(/==|=~/)
+    end
+
     def process_command line
       if line.empty?
         if @repl_prev_line
@@ -1153,10 +1165,10 @@ def process_command line
         @repl_prev_line = line
       end
 
-      /([^\s]+)(?:\s+(.+))?/ =~ line
-      cmd_name, cmd_arg = $1, $2
-
-      if cmd = @commands[cmd_name]
+      if Session.command?(line, commands: @commands)
+        /([^\s]+)(?:\s+(.+))?/ =~ line
+        cmd_name, cmd_arg = $1, $2
+        cmd = @commands[cmd_name]
         check_postmortem      if !cmd.postmortem
         check_unsafe          if cmd.unsafe
         cancel_auto_continue  if cmd.cancel_auto_continue
diff --git a/test/console/session_test.rb b/test/console/session_test.rb
index d17a38ac2..9a7398092 100644
--- a/test/console/session_test.rb
+++ b/test/console/session_test.rb
@@ -1,5 +1,6 @@
 # frozen_string_literal: true
 
+require 'debug/session'
 require_relative '../support/console_test_case'
 
 module DEBUGGER__
@@ -70,4 +71,46 @@ def test_debugger_session_starts_correctly
       end
     end
   end
+
+  class CommandRecognizeTest < ConsoleTestCase
+    def program
+      <<~RUBY
+       1| a = 1
+       2| b = 2
+       3| a = b
+       4| "foo"
+      RUBY
+    end
+
+    def test_is_command
+      commands = { 'n' => true, 'p' => true }
+      command_expressions = ['n', 'p 1', " n \n", " p 1 \n", 'n + 1', 'p == 1']
+      non_command_expressions = ["n\n\n", 'n = 1', 'n ||= 1', 'n =1', "p 1\n.itself"]
+      command_expressions.each do |s|
+        assert_equal true, DEBUGGER__::Session.command?(s, commands: commands)
+      end
+      non_command_expressions.each do |s|
+        assert_equal false, DEBUGGER__::Session.command?(s, commands: commands)
+      end
+    end
+
+    def test_assign_expression_conflicting_with_command_treated_as_expression
+      run_ruby(program, options: "-r debug/start") do
+        assert_line_num(1)
+        type 'n'
+        assert_line_num(2)
+        type '  n  '
+        assert_line_num(3)
+        type 'n = 123000'
+        assert_line_num(3)
+        type 'n += 456'
+        assert_line_num(3)
+        type 'p n'
+        assert_line_text('123456')
+        type 'next'
+        assert_line_num(4)
+        type 'c'
+      end
+    end
+  end
 end