diff --git a/compiler/src/dotty/tools/dotc/transform/patmat/Space.scala b/compiler/src/dotty/tools/dotc/transform/patmat/Space.scala
index 0df81f756925..57ecf0df33ad 100644
--- a/compiler/src/dotty/tools/dotc/transform/patmat/Space.scala
+++ b/compiler/src/dotty/tools/dotc/transform/patmat/Space.scala
@@ -619,7 +619,7 @@ object SpaceEngine {
       case OrType(tp1, tp2)                            => List(tp1, tp2)
       case tp if tp.isRef(defn.BooleanClass)           => List(ConstantType(Constant(true)), ConstantType(Constant(false)))
       case tp if tp.isRef(defn.UnitClass)              => ConstantType(Constant(())) :: Nil
-      case tp @ NamedType(Parts(parts), _)             => parts.map(tp.derivedSelect)
+      case tp @ NamedType(Parts(parts), _)             => if parts.exists(_ eq tp) then ListOfNoType else parts.map(tp.derivedSelect)
       case _: SingletonType                            => ListOfNoType
       case tp if tp.classSymbol.isAllOf(JavaEnum)      => tp.classSymbol.children.map(_.termRef)
         // the class of a java enum value is the enum class, so this must follow SingletonType to not loop infinitely
diff --git a/tests/pos/i19031.ci-reg1.scala b/tests/warn/i19031.ci-reg1.scala
similarity index 91%
rename from tests/pos/i19031.ci-reg1.scala
rename to tests/warn/i19031.ci-reg1.scala
index 3c15a3eb9afc..6e8c92c377ea 100644
--- a/tests/pos/i19031.ci-reg1.scala
+++ b/tests/warn/i19031.ci-reg1.scala
@@ -1,5 +1,3 @@
-//> using options -Werror
-
 sealed trait Mark[T]
 
 trait Foo[T]
diff --git a/tests/pos/i19031.ci-reg2.scala b/tests/warn/i19031.ci-reg2.scala
similarity index 91%
rename from tests/pos/i19031.ci-reg2.scala
rename to tests/warn/i19031.ci-reg2.scala
index e5b12cc17655..a4d5a83fa4dd 100644
--- a/tests/pos/i19031.ci-reg2.scala
+++ b/tests/warn/i19031.ci-reg2.scala
@@ -1,5 +1,3 @@
-//> using options -Werror
-
 trait Outer:
   sealed trait Foo
   case class  Bar1() extends Foo
diff --git a/tests/pos/i19031.scala b/tests/warn/i19031.scala
similarity index 80%
rename from tests/pos/i19031.scala
rename to tests/warn/i19031.scala
index e56744017255..174f459460fd 100644
--- a/tests/pos/i19031.scala
+++ b/tests/warn/i19031.scala
@@ -1,5 +1,3 @@
-//> using options -Werror
-
 sealed trait A:
   class B extends A
 
diff --git a/tests/warn/i19031b.scala b/tests/warn/i19031b.scala
new file mode 100644
index 000000000000..0b6eaff5df1f
--- /dev/null
+++ b/tests/warn/i19031b.scala
@@ -0,0 +1,10 @@
+sealed trait A:
+  class B extends A
+
+class C extends A
+
+class Test:
+  def t1(a: A): Boolean =
+    a match
+      case b: A#B => true
+      case c: C   => true