diff --git a/CHANGELOG.md b/CHANGELOG.md
index 9068f87a5e..3d0ef88301 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -20,6 +20,7 @@
 - Fix accidental removal of `Belt.Result.Ok` and `Belt.Result.Error` constructors in rc.5 https://github.com/rescript-lang/rescript-compiler/pull/6514
 - Add missing check that the runtime representation of variants matches implementation and interface. https://github.com/rescript-lang/rescript-compiler/pull/6513/files
 - GenType: only export types (not values) from module types. https://github.com/rescript-lang/rescript-compiler/pull/6516
+- Fix compiler crash with unboxed variant definition with only 1 constructor. https://github.com/rescript-lang/rescript-compiler/pull/6523
 
 # 11.0.0-rc.7
 
diff --git a/jscomp/ml/typedecl.ml b/jscomp/ml/typedecl.ml
index 344cdd2462..43a8b3f05f 100644
--- a/jscomp/ml/typedecl.ml
+++ b/jscomp/ml/typedecl.ml
@@ -337,6 +337,8 @@ let transl_declaration ~typeRecordAsObject env sdecl id =
   end;
   let unboxed_status =
     match sdecl.ptype_kind with
+    | Ptype_variant [{pcd_args = Pcstr_tuple []; _}] ->
+      unboxed_false_default_false
     | Ptype_variant [{pcd_args = Pcstr_tuple _; _}]
       | Ptype_variant [{pcd_args = Pcstr_record
                           [{pld_mutable = Immutable; _}]; _}]
diff --git a/jscomp/test/UntaggedVariants.js b/jscomp/test/UntaggedVariants.js
index 0ee038afc0..39735c74f6 100644
--- a/jscomp/test/UntaggedVariants.js
+++ b/jscomp/test/UntaggedVariants.js
@@ -583,6 +583,10 @@ var Aliased = {
   test: test
 };
 
+var OnlyOne = {
+  onlyOne: "OnlyOne"
+};
+
 var i = 42;
 
 var i2 = 42.5;
@@ -629,4 +633,5 @@ exports.PromiseSync = PromiseSync;
 exports.Arr = Arr;
 exports.AllInstanceofTypes = AllInstanceofTypes;
 exports.Aliased = Aliased;
+exports.OnlyOne = OnlyOne;
 /* l2 Not a pure module */
diff --git a/jscomp/test/UntaggedVariants.res b/jscomp/test/UntaggedVariants.res
index 65ec308172..0bcfe81208 100644
--- a/jscomp/test/UntaggedVariants.res
+++ b/jscomp/test/UntaggedVariants.res
@@ -427,3 +427,8 @@ module Aliased = {
     }
   }
 }
+
+module OnlyOne = {
+  @unboxed type onlyOne = OnlyOne
+  let onlyOne = OnlyOne
+}
\ No newline at end of file