3 files changed, 42 insertions, 1 deletions
diff --git a/src/compiler/scala/tools/nsc/typechecker/Typers.scala b/src/compiler/scala/tools/nsc/typechecker/Typers.scala
index dfe08c398e..b4c2eb9fe5 100644
--- a/src/compiler/scala/tools/nsc/typechecker/Typers.scala
+++ b/src/compiler/scala/tools/nsc/typechecker/Typers.scala
@@ -2394,7 +2394,7 @@ trait Typers extends Modes with Adaptations with Tags {
         else targs.init
 
       def mkParams(methodSym: Symbol, formals: List[Type] = deriveFormals) =
-        if (formals.isEmpty) { MissingParameterTypeAnonMatchError(tree, pt); Nil }
+        if (formals.isEmpty || !formals.forall(isFullyDefined)) { MissingParameterTypeAnonMatchError(tree, pt); Nil }
         else methodSym newSyntheticValueParams formals
 
       def mkSel(params: List[Symbol]) =
diff --git a/test/files/neg/t6258.check b/test/files/neg/t6258.check
new file mode 100644
index 0000000000..73363d8280
--- /dev/null
+++ b/test/files/neg/t6258.check
@@ -0,0 +1,16 @@
+t6258.scala:2: error: missing parameter type for expanded function
+The argument types of an anonymous function must be fully known. (SLS 8.5)
+Expected type was: PartialFunction[?, Int]
+	val f : PartialFunction[_, Int] = { case a : Int => a } // undefined param
+                                          ^
+t6258.scala:5: error: missing parameter type for expanded function
+The argument types of an anonymous function must be fully known. (SLS 8.5)
+Expected type was: PartialFunction[?,Int]
+	foo { case a : Int => a } // undefined param
+            ^
+t6258.scala:22: error: missing parameter type for expanded function
+The argument types of an anonymous function must be fully known. (SLS 8.5)
+Expected type was: PartialFunction[?,Any]
+  bar[M[Any]] (foo { // undefined param
+                   ^
+three errors found
diff --git a/test/files/neg/t6258.scala b/test/files/neg/t6258.scala
new file mode 100644
index 0000000000..5046a4750a
--- /dev/null
+++ b/test/files/neg/t6258.scala
@@ -0,0 +1,25 @@
+object Test {
+	val f : PartialFunction[_, Int] = { case a : Int => a } // undefined param
+
+	def foo[A](pf: PartialFunction[A, Int]) {};
+	foo { case a : Int => a } // undefined param
+
+	val g : PartialFunction[Int, _] = { case a : Int => a } // okay
+}
+
+
+// Another variation, seen in the wild with Specs2.
+class X {
+  trait Matcher[-T]
+
+  def bar[T](m: Matcher[T]) = null
+  def bar[T](i: Int) = null
+
+  def foo[T](p: PartialFunction[T, Any]): Matcher[T] = null
+
+  case class M[X](a: X)
+
+  bar[M[Any]] (foo { // undefined param
+    case M(_) => null
+  })
+}