diff --git a/lib/rubocop/cop/internal_affairs/single_line_comparison.rb b/lib/rubocop/cop/internal_affairs/single_line_comparison.rb
index 121aa275c03..937f3982992 100644
--- a/lib/rubocop/cop/internal_affairs/single_line_comparison.rb
+++ b/lib/rubocop/cop/internal_affairs/single_line_comparison.rb
@@ -29,20 +29,21 @@ class SingleLineComparison < Base
         extend AutoCorrector
 
         MSG = 'Use `%<preferred>s`.'
-        RESTRICT_ON_SEND = %i[==].freeze
+        RESTRICT_ON_SEND = %i[== !=].freeze
 
         # @!method single_line_comparison(node)
         def_node_matcher :single_line_comparison, <<~PATTERN
           {
-            (send (send $_receiver {:line :first_line}) :== (send _receiver :last_line))
-            (send (send $_receiver :last_line) :== (send _receiver {:line :first_line}))
+            (send (send $_receiver {:line :first_line}) {:== :!=} (send _receiver :last_line))
+            (send (send $_receiver :last_line) {:== :!=} (send _receiver {:line :first_line}))
           }
         PATTERN
 
         def on_send(node)
           return unless (receiver = single_line_comparison(node))
 
-          preferred = "#{extract_receiver(receiver)}.single_line?"
+          bang = node.method?(:!=) ? '!' : ''
+          preferred = "#{bang}#{extract_receiver(receiver)}.single_line?"
 
           add_offense(node, message: format(MSG, preferred: preferred)) do |corrector|
             corrector.replace(node, preferred)
diff --git a/lib/rubocop/cop/layout/redundant_line_break.rb b/lib/rubocop/cop/layout/redundant_line_break.rb
index 4dc136ed88f..d895b3bd2db 100644
--- a/lib/rubocop/cop/layout/redundant_line_break.rb
+++ b/lib/rubocop/cop/layout/redundant_line_break.rb
@@ -101,7 +101,7 @@ def suitable_as_single_line?(node)
           !comment_within?(node) &&
             node.each_descendant(:if, :case, :kwbegin, :def).none? &&
             node.each_descendant(:dstr, :str).none?(&:heredoc?) &&
-            node.each_descendant(:begin).none? { |b| b.first_line != b.last_line }
+            node.each_descendant(:begin).none? { |b| !b.single_line? }
         end
 
         def convertible_block?(node)
diff --git a/lib/rubocop/cop/mixin/check_line_breakable.rb b/lib/rubocop/cop/mixin/check_line_breakable.rb
index b6fdb4d804c..34c5325b286 100644
--- a/lib/rubocop/cop/mixin/check_line_breakable.rb
+++ b/lib/rubocop/cop/mixin/check_line_breakable.rb
@@ -220,7 +220,7 @@ def process_args(args)
       def already_on_multiple_lines?(node)
         return node.first_line != node.arguments.last.last_line if node.def_type?
 
-        node.first_line != node.last_line
+        !node.single_line?
       end
     end
   end
diff --git a/lib/rubocop/cop/style/multiline_in_pattern_then.rb b/lib/rubocop/cop/style/multiline_in_pattern_then.rb
index 7775a83fc27..fa398b87e93 100644
--- a/lib/rubocop/cop/style/multiline_in_pattern_then.rb
+++ b/lib/rubocop/cop/style/multiline_in_pattern_then.rb
@@ -49,7 +49,7 @@ def on_in_pattern(node)
 
         # Requires `then` for write `in` and its body on the same line.
         def require_then?(in_pattern_node)
-          return true if in_pattern_node.pattern.first_line != in_pattern_node.pattern.last_line
+          return true unless in_pattern_node.pattern.single_line?
           return false unless in_pattern_node.body
 
           same_line?(in_pattern_node, in_pattern_node.body)
diff --git a/spec/rubocop/cop/internal_affairs/single_line_comparison_spec.rb b/spec/rubocop/cop/internal_affairs/single_line_comparison_spec.rb
index cfc82a2f92f..162b748b57b 100644
--- a/spec/rubocop/cop/internal_affairs/single_line_comparison_spec.rb
+++ b/spec/rubocop/cop/internal_affairs/single_line_comparison_spec.rb
@@ -89,6 +89,28 @@
     RUBY
   end
 
+  it 'registers and corrects an offense when negative comparing `first_line` with `last_line`' do
+    expect_offense(<<~RUBY)
+      node.first_line != node.last_line
+      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Use `!node.single_line?`.
+    RUBY
+
+    expect_correction(<<~RUBY)
+      !node.single_line?
+    RUBY
+  end
+
+  it 'registers and corrects an offense when negative comparing `last_line` with `first_line`' do
+    expect_offense(<<~RUBY)
+      node.last_line != node.first_line
+      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Use `!node.single_line?`.
+    RUBY
+
+    expect_correction(<<~RUBY)
+      !node.single_line?
+    RUBY
+  end
+
   it 'does not register an offense when comparing the same line' do
     expect_no_offenses(<<~RUBY)
       node.loc.first_line == node.loc.line