diff --git a/compiler/src/dotty/tools/dotc/typer/RefChecks.scala b/compiler/src/dotty/tools/dotc/typer/RefChecks.scala
index 7db3c90e6f17..f87cc6beb237 100644
--- a/compiler/src/dotty/tools/dotc/typer/RefChecks.scala
+++ b/compiler/src/dotty/tools/dotc/typer/RefChecks.scala
@@ -51,7 +51,7 @@ object RefChecks {
       }}
 
       for (name <- defaultMethodNames) {
-        val methods = clazz.info.member(name).alternatives.map(_.symbol)
+        val methods = clazz.thisType.member(name).alternatives.map(_.symbol)
         val haveDefaults = methods.filter(_.hasDefaultParams)
         if (haveDefaults.length > 1) {
           val owners = haveDefaults map (_.owner)
diff --git a/tests/pos/first-class-patterns.scala b/tests/pos/first-class-patterns.scala
new file mode 100644
index 000000000000..98d7faf4d8e7
--- /dev/null
+++ b/tests/pos/first-class-patterns.scala
@@ -0,0 +1,23 @@
+
+  // Trait of all extractors with unapply methods
+  trait Matcher[A, B]:
+    def unapply(x: A): Option[B]
+
+  // An extractor defined by an unappy method
+  object Even extends Matcher[Int, Int]:
+    def unapply(x: Int): Option[Int] =
+      if x % 2 == 0 then Some(x) else None
+
+  // Method using a given extractor in pattern position
+  def collect[A, B](xs: List[A], m: Matcher[A, B]): List[B] =
+    xs match
+      case Nil  => Nil
+      case m(x) :: xs1 => x :: collect(xs1, m)
+      case _ :: xs1 => collect(xs1, m)
+
+  @main def test =
+    val xs = List(1, 2, 3, 4)
+    val ys = collect(xs, Even)
+    println(ys)
+
+
diff --git a/tests/pos/i18555.scala b/tests/pos/i18555.scala
new file mode 100644
index 000000000000..84198409370e
--- /dev/null
+++ b/tests/pos/i18555.scala
@@ -0,0 +1,14 @@
+trait GenericCollectionWithCommands {
+  self: PackSupport =>
+
+  def bar(foo: Int = 1): Any = ???
+  def bar(writer: GenericCollectionWithCommands.this.pack.Writer[Any]): Any = ???
+}
+
+trait PackSupport {
+  val pack: SerializationPack
+}
+
+trait SerializationPack {
+  type Writer[A]
+}
\ No newline at end of file
diff --git a/tests/pos/into-bigint.scala b/tests/pos/into-bigint.scala
new file mode 100644
index 000000000000..d7ecee40b3ba
--- /dev/null
+++ b/tests/pos/into-bigint.scala
@@ -0,0 +1,21 @@
+import language.experimental.into
+
+class BigInt(x: Int):
+  def + (other: into BigInt): BigInt = ???
+  def * (other: into BigInt): BigInt = ???
+
+object BigInt:
+  given Conversion[Int, BigInt] = BigInt(_)
+
+  extension (x: into BigInt)
+    def + (other: BigInt): BigInt = ???
+    def * (other: BigInt): BigInt = ???
+
+@main def Test =
+  val x = BigInt(2)
+  val y = 3
+  val a1 = x + y
+  val a2 = y * x
+  val a3 = x * x
+  val a4 = y + y
+