diff --git a/prism_compile.c b/prism_compile.c
index ffabda7175..876278166b 100644
--- a/prism_compile.c
+++ b/prism_compile.c
@@ -2571,6 +2571,7 @@ pm_compile_defined_expr0(rb_iseq_t *iseq, const pm_node_t *node, LINK_ANCHOR *co
       case PM_SOURCE_LINE_NODE:
       case PM_STRING_NODE:
       case PM_SYMBOL_NODE:
+      case PM_UNLESS_NODE:
       case PM_UNTIL_NODE:
       case PM_WHILE_NODE:
       case PM_X_STRING_NODE:
diff --git a/test/ruby/test_compile_prism.rb b/test/ruby/test_compile_prism.rb
index 1f9ce84bfa..f1274fccf5 100644
--- a/test/ruby/test_compile_prism.rb
+++ b/test/ruby/test_compile_prism.rb
@@ -262,6 +262,7 @@ module Prism
       assert_prism_eval("defined?(class << self; end)")
       assert_prism_eval("defined?(while a != 1; end)")
       assert_prism_eval("defined?(until a == 1; end)")
+      assert_prism_eval("defined?(unless true; 1; end)")
     end
 
     def test_GlobalVariableReadNode