diff --git a/CHANGELOG.md b/CHANGELOG.md
index c1e3971d35a..ba29ba5995e 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -16,6 +16,7 @@
 * [#6668](https://github.com/rubocop-hq/rubocop/issues/6668): Fix autocorrection for `Style/UnneededCondition` when conditional has the `unless` form. ([@mvz][])
 * [#6382](https://github.com/rubocop-hq/rubocop/issues/6382): Fix `Layout/IndentationWidth` with `Layout/EndAlignment` set to start_of_line. ([@dischorde][], [@siegfault][], [@mhelmetag][])
 * [#6710](https://github.com/rubocop-hq/rubocop/issues/6710): Fix `Naming/MemoizedInstanceVariableName` on method starts with underscore. ([@pocke][])
+* [#6722](https://github.com/rubocop-hq/rubocop/issues/6722): Fix an error for `Style/OneLineConditional` when `then` branch has no body. ([@koic][])
 
 ### Changes
 
diff --git a/lib/rubocop/cop/style/one_line_conditional.rb b/lib/rubocop/cop/style/one_line_conditional.rb
index 51751979734..1abda984106 100644
--- a/lib/rubocop/cop/style/one_line_conditional.rb
+++ b/lib/rubocop/cop/style/one_line_conditional.rb
@@ -67,6 +67,8 @@ def to_ternary(node)
         end
 
         def expr_replacement(node)
+          return 'nil' if node.nil?
+
           requires_parentheses?(node) ? "(#{node.source})" : node.source
         end
 
diff --git a/spec/rubocop/cop/style/one_line_conditional_spec.rb b/spec/rubocop/cop/style/one_line_conditional_spec.rb
index 34b066c21e1..34012ca227d 100644
--- a/spec/rubocop/cop/style/one_line_conditional_spec.rb
+++ b/spec/rubocop/cop/style/one_line_conditional_spec.rb
@@ -38,6 +38,13 @@
     end
   end
 
+  context 'one line if/then/else/end when `then` branch has no body' do
+    let(:source) { 'if cond then else dont end' }
+
+    include_examples 'offense', 'if'
+    include_examples 'autocorrect', 'cond ? nil : dont'
+  end
+
   context 'one line if/then/end' do
     let(:source) { 'if cond then run end' }