diff --git a/compiler/src/dotty/tools/dotc/typer/RefChecks.scala b/compiler/src/dotty/tools/dotc/typer/RefChecks.scala
index a79408b756ee..f1e6c1638463 100644
--- a/compiler/src/dotty/tools/dotc/typer/RefChecks.scala
+++ b/compiler/src/dotty/tools/dotc/typer/RefChecks.scala
@@ -1166,7 +1166,9 @@ object RefChecks {
       def targetOfHiddenExtension: Symbol =
         val target =
           val target0 = explicitInfo.firstParamTypes.head // required for extension method, the putative receiver
-          target0.dealiasKeepOpaques.typeSymbol.info
+          target0.dealiasKeepOpaques.typeSymbol.info match
+          case tb: AliasingBounds => tb.alias
+          case tp => tp
         val member = target.nonPrivateMember(sym.name)
           .filterWithPredicate: member =>
             member.symbol.isPublic && memberHidesMethod(member)
diff --git a/tests/pos/i23666.scala b/tests/pos/i23666.scala
new file mode 100644
index 000000000000..197008b1776c
--- /dev/null
+++ b/tests/pos/i23666.scala
@@ -0,0 +1,14 @@
+
+type Tuple = scala.Tuple
+type Any = scala.Any
+
+infix type =:= [A, B] = A => B
+
+object `=:=` :
+   given [A] => A =:= A = a => a
+
+extension [T <: Tuple] (tuple: T)
+
+   def reverse[A, B](using ev: T =:= (A, B)): (B, A) = 
+      val ab = ev(tuple)
+      (ab._2, ab._1)