diff --git a/compiler/src/dotty/tools/dotc/core/TypeComparer.scala b/compiler/src/dotty/tools/dotc/core/TypeComparer.scala
index c8e00686e62b..1f3806fa0cc4 100644
--- a/compiler/src/dotty/tools/dotc/core/TypeComparer.scala
+++ b/compiler/src/dotty/tools/dotc/core/TypeComparer.scala
@@ -3187,9 +3187,11 @@ class TypeComparer(@constructorOnly initctx: Context) extends ConstraintHandling
         else child
       }.filter(child => child.exists && child != cls)
 
-    // TODO? Special-case for Nothing and Null? We probably need Nothing/Null disjoint from Nothing/Null
     def eitherDerivesFromOther(cls1: Symbol, cls2: Symbol): Boolean =
-      cls1.derivesFrom(cls2) || cls2.derivesFrom(cls1)
+      if cls1 eq cls2 then
+        cls1 != defn.NothingClass && cls1 != defn.NullClass
+      else
+        cls1.derivesFrom(cls2) || cls2.derivesFrom(cls1)
 
     def smallestNonTraitBase(cls: Symbol): Symbol =
       cls.asClass.baseClasses.find(!_.is(Trait)).get
diff --git a/compiler/test/dotc/pos-test-pickling.blacklist b/compiler/test/dotc/pos-test-pickling.blacklist
index d6f962176ecc..b68ac7fc3b6e 100644
--- a/compiler/test/dotc/pos-test-pickling.blacklist
+++ b/compiler/test/dotc/pos-test-pickling.blacklist
@@ -67,6 +67,7 @@ mt-redux-norm.perspective.scala
 i18211.scala
 10867.scala
 named-tuples1.scala
+i20897.scala
 
 # Opaque type
 i5720.scala
@@ -134,4 +135,3 @@ parsercombinators-new-syntax.scala
 hylolib-deferred-given
 hylolib-cb
 hylolib
-
diff --git a/tests/pos/i20897.scala b/tests/pos/i20897.scala
new file mode 100644
index 000000000000..ecfac5b1615e
--- /dev/null
+++ b/tests/pos/i20897.scala
@@ -0,0 +1,10 @@
+object Test:
+  type Disj[A, B] =
+    A match
+      case B => true
+      case _ => false
+
+  def f(a: Disj[1 | Nothing, 2 | Nothing]): Unit = ()
+
+  val t = f(false)
+end Test