diff --git a/core/shared/src/main/scala/dev/tauri/choam/refs/RefLike.scala b/core/shared/src/main/scala/dev/tauri/choam/refs/RefLike.scala
index d81631581..d2e8b1c06 100644
--- a/core/shared/src/main/scala/dev/tauri/choam/refs/RefLike.scala
+++ b/core/shared/src/main/scala/dev/tauri/choam/refs/RefLike.scala
@@ -29,10 +29,12 @@ trait RefLike[A] {
 
   def updWith[B, C](f: (A, B) => Axn[(A, C)]): Rxn[B, C]
 
-  // derived (but overridden for performance):
+  // derivable (but primitive for performance):
 
-  def upd[B, C](f: (A, B) => (A, C)): Rxn[B, C] =
-    updWith[B, C] { (a, b) => Axn.pure(f(a, b)) }
+  def upd[B, C](f: (A, B) => (A, C)): Rxn[B, C]
+  // Note: in theory this could be implemented as
+  // `updWith[B, C] { (a, b) => Axn.pure(f(a, b)) }`,
+  // but we rather have it as a primitive.
 
   // derived:
 
diff --git a/data/jvm/src/main/scala/dev/tauri/choam/data/Ttrie.scala b/data/jvm/src/main/scala/dev/tauri/choam/data/Ttrie.scala
index 05fd1eec4..0e19f5e3f 100644
--- a/data/jvm/src/main/scala/dev/tauri/choam/data/Ttrie.scala
+++ b/data/jvm/src/main/scala/dev/tauri/choam/data/Ttrie.scala
@@ -274,7 +274,8 @@ private final class Ttrie[K, V] private (
     final def get: Axn[V] =
       self.get.provide(key).map(_.getOrElse(default))
 
-    // TODO: maybe override `upd` and/or `getAndSet` if we can make it faster than the default impl.
+    final def upd[B, C](f: (V, B) => (V, C)): B =#> C =
+      updWith[B, C] { (v, b) => Axn.pure(f(v, b)) }
 
     final def updWith[B, C](f: (V, B) => Axn[(V, C)]): B =#> C = {
       getRefWithKey(key).flatMap { ref =>
diff --git a/data/shared/src/main/scala/dev/tauri/choam/data/SimpleMap.scala b/data/shared/src/main/scala/dev/tauri/choam/data/SimpleMap.scala
index 147287ea1..cd786290b 100644
--- a/data/shared/src/main/scala/dev/tauri/choam/data/SimpleMap.scala
+++ b/data/shared/src/main/scala/dev/tauri/choam/data/SimpleMap.scala
@@ -103,7 +103,7 @@ private final class SimpleMap[K, V] private (
     final def get: Axn[V] =
       self.get.provide(key).map(_.getOrElse(default))
 
-    final override def upd[B, C](f: (V, B) => (V, C)): B =#> C = {
+    final def upd[B, C](f: (V, B) => (V, C)): B =#> C = {
       Rxn.computed[B, C] { (b: B) =>
         repr.modify { hm =>
           val currVal = hm.getOrElse(key, default)
diff --git a/data/shared/src/main/scala/dev/tauri/choam/data/SimpleOrderedMap.scala b/data/shared/src/main/scala/dev/tauri/choam/data/SimpleOrderedMap.scala
index 4201bb153..cb15acf1a 100644
--- a/data/shared/src/main/scala/dev/tauri/choam/data/SimpleOrderedMap.scala
+++ b/data/shared/src/main/scala/dev/tauri/choam/data/SimpleOrderedMap.scala
@@ -105,7 +105,7 @@ private final class SimpleOrderedMap[K, V] private (
     final def get: Axn[V] =
       self.get.provide(key).map(_.getOrElse(default))
 
-    final override def upd[B, C](f: (V, B) => (V, C)): B =#> C = {
+    final def upd[B, C](f: (V, B) => (V, C)): B =#> C = {
       Rxn.computed[B, C] { (b: B) =>
         repr.modify { am =>
           val currVal = am.get(key).getOrElse(default)