diff --git a/sbt-bridge/src/dotty/tools/xsbt/PositionBridge.java b/sbt-bridge/src/dotty/tools/xsbt/PositionBridge.java
index 2f20609578db..075efd5b53e6 100644
--- a/sbt-bridge/src/dotty/tools/xsbt/PositionBridge.java
+++ b/sbt-bridge/src/dotty/tools/xsbt/PositionBridge.java
@@ -39,6 +39,10 @@ public Optional<Integer> pointer() {
     public Optional<String> pointerSpace() {
       return Optional.empty();
     }
+
+    public String toString() {
+      return "";
+    }
   };
 
   public PositionBridge(SourcePosition pos, SourceFile src) {
@@ -116,4 +120,58 @@ public Optional<String> pointerSpace() {
       result.append(lineContent.charAt(i) == '\t' ? '\t' : ' ');
     return Optional.of(result.toString());
   }
+
+  @Override
+  public String toString() {
+      return pos.toString();
+  }
+  
+  @Override
+  public Optional<Integer> startOffset() {
+    if (src.content().length == 0)
+      return Optional.empty();
+    else
+      return Optional.of(pos.start());
+  }
+
+  @Override
+  public Optional<Integer> endOffset() {
+    if (src.content().length == 0)
+      return Optional.empty();
+    else
+      return Optional.of(pos.end());
+  }
+
+  @Override
+  public Optional<Integer> startLine() {
+    if (src.content().length == 0)
+      return Optional.empty();
+    else
+      return Optional.of(pos.startLine() + 1);
+  }
+
+  @Override
+  public Optional<Integer> endLine() {
+    if (src.content().length == 0)
+      return Optional.empty();
+    else
+      return Optional.of(pos.endLine() + 1);
+  }
+
+  @Override
+  public Optional<Integer> startColumn() {
+    if (src.content().length == 0)
+      return Optional.empty();
+    else
+      return Optional.of(pos.startColumn());
+  }
+
+  @Override
+  public Optional<Integer> endColumn() {
+    if (src.content().length == 0)
+      return Optional.empty();
+    else
+      return Optional.of(pos.endColumn());
+  }
+
 }
diff --git a/tests/neg/i12640.scala b/tests/neg/i12640.scala
deleted file mode 100644
index 7946525deeeb..000000000000
--- a/tests/neg/i12640.scala
+++ /dev/null
@@ -1,17 +0,0 @@
-package x
-
-trait CpsMonad[F[_]]:
-  def pure[A](x:A): F[A]
-  def flatMap[A,B](fa:F[A])(f: A=>F[B]): F[B]
-
-abstract sealed class CpsStream[-F[_],+T]
-
-case class Cons[F[_],T](head:T, tailFun: ()=>F[CpsStream[F,T]]) extends CpsStream[F,T]
-
-case class Empty[F[_]]() extends CpsStream[F,Nothing]
-
-def unfold[S,F[_]:CpsMonad,T](s0:S)(f:S => F[Option[(S,T)]]):F[CpsStream[F,T]] =
-      summon[CpsMonad[F]].flatMap(f(s0)){
-         case Some(s1,a) => Cons(a, () => unfold(s1,f))  // error // error
-         case None => summon[CpsMonad[F]].pure(Empty[F]())
-      }
\ No newline at end of file