diff --git a/compiler/src/dotty/tools/dotc/cc/SepCheck.scala b/compiler/src/dotty/tools/dotc/cc/SepCheck.scala
index 7ca972b1ad63..d3eaf273dcbc 100644
--- a/compiler/src/dotty/tools/dotc/cc/SepCheck.scala
+++ b/compiler/src/dotty/tools/dotc/cc/SepCheck.scala
@@ -256,7 +256,7 @@ class SepChecker(checker: CheckCaptures.CheckerAPI) extends tpd.TreeTraverser:
       (formal, arg) <- mt.paramInfos.zip(args)
       dep <- formal.captureSet.elems.toList
     do
-      val referred = dep match
+      val referred = dep.stripReach match
         case dep: TermParamRef =>
           argMap(dep.binder)(dep.paramNum) :: Nil
         case dep: ThisType if dep.cls == fn.symbol.owner =>
diff --git a/project/Build.scala b/project/Build.scala
index 58995ce8ad85..31a5330afad4 100644
--- a/project/Build.scala
+++ b/project/Build.scala
@@ -1223,7 +1223,7 @@ object Build {
     settings(scala2LibraryBootstrappedSettings).
     settings(
       moduleName := "scala2-library-cc",
-      scalacOptions ++= Seq("-Ycheck:all", "-source", "3.7")
+      scalacOptions ++= Seq("-Ycheck:all", "-source", "3.8")
     )
 
   lazy val scala2LibraryBootstrappedSettings = Seq(
diff --git a/tests/neg-custom-args/captures/box-adapt-cases.scala b/tests/neg-custom-args/captures/box-adapt-cases.scala
index 55371c4e50b7..dbc735dbd4f2 100644
--- a/tests/neg-custom-args/captures/box-adapt-cases.scala
+++ b/tests/neg-custom-args/captures/box-adapt-cases.scala
@@ -1,4 +1,4 @@
-import language.`3.7` // sepchecks on
+import language.`3.8` // sepchecks on
 trait Cap { def use(): Int }
 
 def test1(): Unit = {
diff --git a/tests/neg-custom-args/captures/depfun-reach.scala b/tests/neg-custom-args/captures/depfun-reach.scala
index 6c198ff8fd9f..798c290f9b4a 100644
--- a/tests/neg-custom-args/captures/depfun-reach.scala
+++ b/tests/neg-custom-args/captures/depfun-reach.scala
@@ -1,6 +1,6 @@
 import language.experimental.captureChecking
 import caps.cap
-import language.`3.7` // sepchecks on
+import language.`3.8` // sepchecks on
 def test(io: Object^, async: Object^) =
   def compose(op: List[(() ->{cap} Unit, () ->{cap} Unit)]): List[() ->{op*} Unit] =
     List(() => op.foreach((f,g) => { f(); g() }))
diff --git a/tests/neg-custom-args/captures/existential-mapping.scala b/tests/neg-custom-args/captures/existential-mapping.scala
index aa45e60cdabc..3ed0462c197b 100644
--- a/tests/neg-custom-args/captures/existential-mapping.scala
+++ b/tests/neg-custom-args/captures/existential-mapping.scala
@@ -1,5 +1,5 @@
 import language.experimental.captureChecking
-import language.`3.7` // sepchecks on
+import language.`3.8` // sepchecks on
 class A
 class C
 type Fun[X] = (x: C^) -> X
diff --git a/tests/neg-custom-args/captures/i19330.scala b/tests/neg-custom-args/captures/i19330.scala
index 23fcfa0ffc4f..855a5c654285 100644
--- a/tests/neg-custom-args/captures/i19330.scala
+++ b/tests/neg-custom-args/captures/i19330.scala
@@ -1,4 +1,4 @@
-import language.`3.7` // sepchecks on
+import language.`3.8` // sepchecks on
 import language.experimental.captureChecking
 
 
diff --git a/tests/neg-custom-args/captures/i21614.scala b/tests/neg-custom-args/captures/i21614.scala
index d21fb2f5d3a0..f33c92b9a971 100644
--- a/tests/neg-custom-args/captures/i21614.scala
+++ b/tests/neg-custom-args/captures/i21614.scala
@@ -1,7 +1,7 @@
 import language.experimental.captureChecking
 import caps.Capability
 import caps.use
-import language.`3.7` // sepchecks on
+import language.`3.8` // sepchecks on
 trait List[+T]:
   def map[U](f: T => U): List[U]
 
diff --git a/tests/neg-custom-args/captures/lazyref.scala b/tests/neg-custom-args/captures/lazyref.scala
index 52e274b65175..8b21e04a7dc8 100644
--- a/tests/neg-custom-args/captures/lazyref.scala
+++ b/tests/neg-custom-args/captures/lazyref.scala
@@ -1,4 +1,4 @@
-import language.`3.7` // sepchecks on
+import language.`3.8` // sepchecks on
 class CC
 type Cap = CC^
 
diff --git a/tests/neg-custom-args/captures/outer-var.scala b/tests/neg-custom-args/captures/outer-var.scala
index 4ec19d8f8971..52d4a1b3e91f 100644
--- a/tests/neg-custom-args/captures/outer-var.scala
+++ b/tests/neg-custom-args/captures/outer-var.scala
@@ -1,4 +1,4 @@
-import language.`3.7` // sepchecks on
+import language.`3.8` // sepchecks on
 class CC
 type Cap = CC^
 
diff --git a/tests/neg-custom-args/captures/reaches.scala b/tests/neg-custom-args/captures/reaches.scala
index c82ada78f17b..c7c19d82a376 100644
--- a/tests/neg-custom-args/captures/reaches.scala
+++ b/tests/neg-custom-args/captures/reaches.scala
@@ -1,4 +1,4 @@
-import caps.use; import language.`3.7` // sepchecks on
+import caps.use; import language.`3.8` // sepchecks on
 class File:
   def write(): Unit = ???
 
diff --git a/tests/neg-custom-args/captures/reaches2.check b/tests/neg-custom-args/captures/reaches2.check
index 1e921ee92072..74223963dde9 100644
--- a/tests/neg-custom-args/captures/reaches2.check
+++ b/tests/neg-custom-args/captures/reaches2.check
@@ -1,10 +1,25 @@
--- Error: tests/neg-custom-args/captures/reaches2.scala:8:10 -----------------------------------------------------------
-8 |  ps.map((x, y) => compose1(x, y)) // error // error
-  |          ^
-  |reference ps* is not included in the allowed capture set {}
-  |of an enclosing function literal with expected type ((box A ->{ps*} A, box A ->{ps*} A)) -> box (x$0: A^?) ->? A^?
--- Error: tests/neg-custom-args/captures/reaches2.scala:8:13 -----------------------------------------------------------
-8 |  ps.map((x, y) => compose1(x, y)) // error // error
-  |             ^
-  |reference ps* is not included in the allowed capture set {}
-  |of an enclosing function literal with expected type ((box A ->{ps*} A, box A ->{ps*} A)) -> box (x$0: A^?) ->? A^?
+-- Error: tests/neg-custom-args/captures/reaches2.scala:10:10 ----------------------------------------------------------
+10 |  ps.map((x, y) => compose1(x, y)) // error // error // error
+   |          ^
+   |reference ps* is not included in the allowed capture set {}
+   |of an enclosing function literal with expected type ((box A ->{ps*} A, box A ->{ps*} A)) -> box (x$0: A^?) ->? A^?
+-- Error: tests/neg-custom-args/captures/reaches2.scala:10:13 ----------------------------------------------------------
+10 |  ps.map((x, y) => compose1(x, y)) // error // error // error
+   |             ^
+   |reference ps* is not included in the allowed capture set {}
+   |of an enclosing function literal with expected type ((box A ->{ps*} A, box A ->{ps*} A)) -> box (x$0: A^?) ->? A^?
+-- Error: tests/neg-custom-args/captures/reaches2.scala:10:31 ----------------------------------------------------------
+10 |  ps.map((x, y) => compose1(x, y)) // error // error // error
+   |                               ^
+   |                               Separation failure: argument of type  (x$0: A) ->{y} box A^?
+   |                               to method compose1: [A, B, C](f: A => B, g: B => C): A ->{f, g} C
+   |                               corresponds to capture-polymorphic formal parameter g of type  box A^? => box A^?
+   |                               and captures {ps*}, but this capability is also passed separately
+   |                               in the first argument with type  (x$0: A) ->{x} box A^?.
+   |
+   |                                 Capture set of first argument         : {x}
+   |                                 Hidden set of current argument        : {y}
+   |                                 Footprint of first argument           : {x, ps*}
+   |                                 Hidden footprint of current argument  : {y, ps*}
+   |                                 Declared footprint of current argument: {}
+   |                                 Undeclared overlap of footprints      : {ps*}
diff --git a/tests/neg-custom-args/captures/reaches2.scala b/tests/neg-custom-args/captures/reaches2.scala
index f2447b8c8795..9620d57d42e6 100644
--- a/tests/neg-custom-args/captures/reaches2.scala
+++ b/tests/neg-custom-args/captures/reaches2.scala
@@ -1,3 +1,5 @@
+import language.`3.8` // sepchecks on
+
 class List[+A]:
   def map[B](f: A -> B): List[B] = ???
 
@@ -5,5 +7,5 @@ def compose1[A, B, C](f: A => B, g: B => C): A ->{f, g} C =
   z => g(f(z))
 
 def mapCompose[A](ps: List[(A => A, A => A)]): List[A ->{ps*} A] =
-  ps.map((x, y) => compose1(x, y)) // error // error
+  ps.map((x, y) => compose1(x, y)) // error // error // error
 
diff --git a/tests/neg-custom-args/captures/unsound-reach-2.scala b/tests/neg-custom-args/captures/unsound-reach-2.scala
index 90dd3824099f..2c54a8dfec93 100644
--- a/tests/neg-custom-args/captures/unsound-reach-2.scala
+++ b/tests/neg-custom-args/captures/unsound-reach-2.scala
@@ -1,4 +1,4 @@
-import language.experimental.captureChecking; import language.`3.7` // sepchecks on
+import language.experimental.captureChecking; import language.`3.8` // sepchecks on
 trait Consumer[-T]:
   def apply(x: T): Unit
 
diff --git a/tests/neg-custom-args/captures/unsound-reach-3.scala b/tests/neg-custom-args/captures/unsound-reach-3.scala
index 0992dffb63ff..f3dfa77186db 100644
--- a/tests/neg-custom-args/captures/unsound-reach-3.scala
+++ b/tests/neg-custom-args/captures/unsound-reach-3.scala
@@ -1,6 +1,6 @@
 
 
-import language.experimental.captureChecking; import language.`3.7` // sepchecks on
+import language.experimental.captureChecking; import language.`3.8` // sepchecks on
 trait File:
   def close(): Unit
 
diff --git a/tests/neg-custom-args/captures/unsound-reach-4.scala b/tests/neg-custom-args/captures/unsound-reach-4.scala
index bba09c0286e3..7f9375220098 100644
--- a/tests/neg-custom-args/captures/unsound-reach-4.scala
+++ b/tests/neg-custom-args/captures/unsound-reach-4.scala
@@ -1,6 +1,6 @@
 
 
-import language.experimental.captureChecking; import language.`3.7` // sepchecks on
+import language.experimental.captureChecking; import language.`3.8` // sepchecks on
 trait File:
   def close(): Unit
 
diff --git a/tests/neg-custom-args/captures/vars.scala b/tests/neg-custom-args/captures/vars.scala
index fc0de7354dd3..234fa9c9da2f 100644
--- a/tests/neg-custom-args/captures/vars.scala
+++ b/tests/neg-custom-args/captures/vars.scala
@@ -1,4 +1,4 @@
-import language.`3.7` // sepchecks on
+import language.`3.8` // sepchecks on
 
 class CC
 type Cap = CC^
diff --git a/tests/pos-custom-args/captures/i15749a.scala b/tests/pos-custom-args/captures/i15749a.scala
index 184f980d6d70..d562763e2807 100644
--- a/tests/pos-custom-args/captures/i15749a.scala
+++ b/tests/pos-custom-args/captures/i15749a.scala
@@ -1,5 +1,6 @@
 import caps.cap
 import caps.use
+import language.`3.8` // sepchecks on
 
 class Unit
 object u extends Unit
@@ -13,7 +14,7 @@ def test =
   def wrapper[T](x: T): Wrapper[T] = Wrapper:
     [X] => (op: T ->{cap} X) => op(x)
 
-  def strictMap[A <: Top,  B <: Top](mx: Wrapper[A])(f: A ->{cap} B): Wrapper[B] =
+  def strictMap[A <: Top,  B <: Top](mx: Wrapper[A])(f: A ->{cap, mx*} B): Wrapper[B] =
     mx.value((x: A) => wrapper(f(x)))
 
   def force[A](thunk: Unit ->{cap} A): A = thunk(u)