diff --git a/compiler/src/dotty/tools/dotc/ast/Desugar.scala b/compiler/src/dotty/tools/dotc/ast/Desugar.scala
index e1a6b97fc7d3..e66c71731b4f 100644
--- a/compiler/src/dotty/tools/dotc/ast/Desugar.scala
+++ b/compiler/src/dotty/tools/dotc/ast/Desugar.scala
@@ -1605,9 +1605,10 @@ object desugar {
 
   /** Translate tuple expressions
    *
-   *     ()             ==>   ()
-   *     (t)            ==>   t
-   *     (t1, ..., tN)  ==>   TupleN(t1, ..., tN)
+   *     ()                       ==>   ()
+   *     (t)                      ==>   t
+   *     (t1, ..., tN)            ==>   TupleN(t1, ..., tN)
+   *     (n1 = t1, ..., nN = tN)  ==>   NamedTuple.build[(n1, ..., nN)]()(TupleN(t1, ..., tN))
    */
   def tuple(tree: Tuple, pt: Type)(using Context): Tree =
     var elems = checkWellFormedTupleElems(tree.trees)
diff --git a/compiler/src/dotty/tools/dotc/reporting/ErrorMessageID.scala b/compiler/src/dotty/tools/dotc/reporting/ErrorMessageID.scala
index db523c879ea2..6d0a85b3ef0f 100644
--- a/compiler/src/dotty/tools/dotc/reporting/ErrorMessageID.scala
+++ b/compiler/src/dotty/tools/dotc/reporting/ErrorMessageID.scala
@@ -216,6 +216,7 @@ enum ErrorMessageID(val isActive: Boolean = true) extends java.lang.Enum[ErrorMe
   case FinalLocalDefID // errorNumber: 200
   case NonNamedArgumentInJavaAnnotationID // errorNumber: 201
   case QuotedTypeMissingID // errorNumber: 202
+  case AmbiguousNamedTupleAssignmentID // errorNumber: 203
 
   def errorNumber = ordinal - 1
 
diff --git a/compiler/src/dotty/tools/dotc/reporting/messages.scala b/compiler/src/dotty/tools/dotc/reporting/messages.scala
index 97cd70113c2e..3b7fba1cb52d 100644
--- a/compiler/src/dotty/tools/dotc/reporting/messages.scala
+++ b/compiler/src/dotty/tools/dotc/reporting/messages.scala
@@ -3343,3 +3343,12 @@ final class QuotedTypeMissing(tpe: Type)(using Context) extends StagingMessage(Q
         |"""
 
 end QuotedTypeMissing
+
+final class AmbiguousNamedTupleAssignment(key: Name, value: untpd.Tree)(using Context) extends SyntaxMsg(AmbiguousNamedTupleAssignmentID):
+  override protected def msg(using Context): String =
+    i"""Ambiguous syntax: this is interpreted as a named tuple with one element,
+      |not as an assignment.
+      |
+      |To assign a value, use curly braces: `{${key} = ${value}}`."""
+  
+  override protected def explain(using Context): String = ""
diff --git a/compiler/src/dotty/tools/dotc/typer/Typer.scala b/compiler/src/dotty/tools/dotc/typer/Typer.scala
index f20c2d313ec7..554e9f1c2f51 100644
--- a/compiler/src/dotty/tools/dotc/typer/Typer.scala
+++ b/compiler/src/dotty/tools/dotc/typer/Typer.scala
@@ -3395,6 +3395,7 @@ class Typer(@constructorOnly nestingLevel: Int = 0) extends Namer
   /** Translate tuples of all arities */
   def typedTuple(tree: untpd.Tuple, pt: Type)(using Context): Tree =
     val tree1 = desugar.tuple(tree, pt)
+    checkAmbiguousNamedTupleAssignment(tree)
     if tree1 ne tree then typed(tree1, pt)
     else
       val arity = tree.trees.length
@@ -3420,6 +3421,20 @@ class Typer(@constructorOnly nestingLevel: Int = 0) extends Namer
           val resTpe = TypeOps.nestedPairs(elemTpes)
           app1.cast(resTpe)
 
+ /** Checks if `tree` is a named tuple with one element that could be
+  *  interpreted as an assignment, such as `(x = 1)`. If so, issues a warning.
+  */
+  def checkAmbiguousNamedTupleAssignment(tree: untpd.Tuple)(using Context): Unit =
+    tree.trees match
+      case List(NamedArg(name, value)) =>
+        val tmpCtx = ctx.fresh.setNewTyperState()
+        typedAssign(untpd.Assign(untpd.Ident(name), value), WildcardType)(using tmpCtx)
+        if !tmpCtx.reporter.hasErrors then
+          // If there are no errors typing the above, then the named tuple is
+          // ambiguous and we issue a warning.
+          report.migrationWarning(AmbiguousNamedTupleAssignment(name, value), tree.srcPos)
+      case _ => ()
+
   /** Retrieve symbol attached to given tree */
   protected def retrieveSym(tree: untpd.Tree)(using Context): Symbol = tree.removeAttachment(SymOfTree) match {
     case Some(sym) =>
diff --git a/tests/pos/21681d.scala b/tests/pos/21681d.scala
new file mode 100644
index 000000000000..97a01dec74aa
--- /dev/null
+++ b/tests/pos/21681d.scala
@@ -0,0 +1,16 @@
+def test1() =
+  class Person:
+    def age: Int = ???
+    def age_=(x: Int): Unit = ???
+
+  val person = Person()
+  
+  (person.age = 29) // no warn (interpreted as `person.age_=(29)`)
+
+def test2() =
+  class Person:
+    var age: Int = 28
+
+  val person = Person()
+  
+  (person.age = 29) // no warn (interpreted as `person.age_=(29)`)
diff --git a/tests/warn/21681.check b/tests/warn/21681.check
new file mode 100644
index 000000000000..e86ce4e36134
--- /dev/null
+++ b/tests/warn/21681.check
@@ -0,0 +1,7 @@
+-- [E203] Syntax Migration Warning: tests/warn/21681.scala:3:2 ---------------------------------------------------------
+3 |  (age = 29) // warn
+  |  ^^^^^^^^^^
+  |  Ambiguous syntax: this is interpreted as a named tuple with one element,
+  |  not as an assignment.
+  |
+  |  To assign a value, use curly braces: `{age = 29}`.
diff --git a/tests/warn/21681.scala b/tests/warn/21681.scala
new file mode 100644
index 000000000000..76a19c96e1cb
--- /dev/null
+++ b/tests/warn/21681.scala
@@ -0,0 +1,3 @@
+def main() =
+  var age: Int = 28
+  (age = 29) // warn
diff --git a/tests/warn/21681b.check b/tests/warn/21681b.check
new file mode 100644
index 000000000000..32760e00ebb6
--- /dev/null
+++ b/tests/warn/21681b.check
@@ -0,0 +1,7 @@
+-- [E203] Syntax Migration Warning: tests/warn/21681b.scala:3:2 --------------------------------------------------------
+3 |  (age = 29) // warn
+  |  ^^^^^^^^^^
+  |  Ambiguous syntax: this is interpreted as a named tuple with one element,
+  |  not as an assignment.
+  |
+  |  To assign a value, use curly braces: `{age = 29}`.
diff --git a/tests/warn/21681b.scala b/tests/warn/21681b.scala
new file mode 100644
index 000000000000..710d69b0dd23
--- /dev/null
+++ b/tests/warn/21681b.scala
@@ -0,0 +1,3 @@
+object Test:
+  var age: Int = 28
+  (age = 29) // warn
diff --git a/tests/warn/21681c.check b/tests/warn/21681c.check
new file mode 100644
index 000000000000..11c427f87cfe
--- /dev/null
+++ b/tests/warn/21681c.check
@@ -0,0 +1,7 @@
+-- [E203] Syntax Migration Warning: tests/warn/21681c.scala:5:2 --------------------------------------------------------
+5 |  (age = 29) // warn
+  |  ^^^^^^^^^^
+  |  Ambiguous syntax: this is interpreted as a named tuple with one element,
+  |  not as an assignment.
+  |
+  |  To assign a value, use curly braces: `{age = 29}`.
diff --git a/tests/warn/21681c.scala b/tests/warn/21681c.scala
new file mode 100644
index 000000000000..5e2eae11708c
--- /dev/null
+++ b/tests/warn/21681c.scala
@@ -0,0 +1,5 @@
+object Test:
+  def age: Int = ???
+  def age_=(x: Int): Unit = ()
+  age = 29
+  (age = 29) // warn
diff --git a/tests/warn/21770.check b/tests/warn/21770.check
new file mode 100644
index 000000000000..0899f11d6ca5
--- /dev/null
+++ b/tests/warn/21770.check
@@ -0,0 +1,7 @@
+-- [E203] Syntax Migration Warning: tests/warn/21770.scala:5:9 ---------------------------------------------------------
+5 |  f(i => (cache = Some(i))) // warn
+  |         ^^^^^^^^^^^^^^^^^
+  |         Ambiguous syntax: this is interpreted as a named tuple with one element,
+  |         not as an assignment.
+  |
+  |         To assign a value, use curly braces: `{cache = Some(i)}`.
diff --git a/tests/warn/21770.scala b/tests/warn/21770.scala
new file mode 100644
index 000000000000..9696a31d6ba8
--- /dev/null
+++ b/tests/warn/21770.scala
@@ -0,0 +1,5 @@
+def f(g: Int  => Unit) = g(0)
+
+def test = 
+  var cache: Option[Int] = None
+  f(i => (cache = Some(i))) // warn