diff --git a/src/compiler/scala/tools/nsc/Global.scala b/src/compiler/scala/tools/nsc/Global.scala
index dc3bfd62a5ce..a80c5dbf4d51 100644
--- a/src/compiler/scala/tools/nsc/Global.scala
+++ b/src/compiler/scala/tools/nsc/Global.scala
@@ -1016,11 +1016,20 @@ class Global(var currentSettings: Settings, reporter0: Reporter)
     && rootMirror.isMirrorInitialized
   )
   override def isPastTyper = isPast(currentRun.typerPhase)
+  def isBeforeErasure      = isBefore(currentRun.erasurePhase)
   def isPast(phase: Phase) = (
        (curRun ne null)
     && isGlobalInitialized // defense against init order issues
     && (globalPhase.id > phase.id)
   )
+  def isBefore(phase: Phase) = (
+       (curRun ne null)
+    && isGlobalInitialized // defense against init order issues
+    && (phase match {
+      case NoPhase => true // if phase is NoPhase then that phase ain't comin', so we're "before it"
+      case _       => globalPhase.id < phase.id
+    })
+  )
 
   // TODO - trim these to the absolute minimum.
   @inline final def exitingErasure[T](op: => T): T        = exitingPhase(currentRun.erasurePhase)(op)
diff --git a/src/compiler/scala/tools/nsc/typechecker/Typers.scala b/src/compiler/scala/tools/nsc/typechecker/Typers.scala
index b5538dfb2441..7644604902dd 100644
--- a/src/compiler/scala/tools/nsc/typechecker/Typers.scala
+++ b/src/compiler/scala/tools/nsc/typechecker/Typers.scala
@@ -1240,9 +1240,9 @@ trait Typers extends Adaptations with Tags with TypersTracking with PatternTyper
           inferExprAlternative(tree, pt)
           adaptAfterOverloadResolution(tree, mode, pt, original)
         case NullaryMethodType(restpe) => // (2)
-          val resTpDeconst =
-            if (isPastTyper || (tree.symbol.isAccessor && tree.symbol.hasFlag(STABLE) && treeInfo.isExprSafeToInline(tree))) restpe
-            else restpe.deconst
+          val resTpDeconst = // only keep the result type as a constant (foldable) type when before erasure & it's safe to inline/fold
+            if (isBeforeErasure && tree.symbol.isAccessor && tree.symbol.hasFlag(STABLE) && treeInfo.isExprSafeToInline(tree)) restpe
+            else restpe.deconst // otherwise deconst-ify, so we don't constant fold it
           adapt(tree setType resTpDeconst, mode, pt, original)
         case TypeRef(_, ByNameParamClass, arg :: Nil) if mode.inExprMode => // (2)
           adapt(tree setType arg, mode, pt, original)
diff --git a/test/files/run/patmat-no-inline-isEmpty.check b/test/files/run/patmat-no-inline-isEmpty.check
new file mode 100644
index 000000000000..60ed79c25c04
--- /dev/null
+++ b/test/files/run/patmat-no-inline-isEmpty.check
@@ -0,0 +1,36 @@
+[[syntax trees at end of                    patmat]] // newSource1.scala
+package <empty> {
+  object A extends scala.AnyRef {
+    def <init>(): A.type = {
+      A.super.<init>();
+      ()
+    };
+    def unapplySeq(a: Int): Wrap = new Wrap(a)
+  };
+  class T extends scala.AnyRef {
+    def <init>(): T = {
+      T.super.<init>();
+      ()
+    };
+    def t: Any = {
+      case <synthetic> val x1: Int(2) = 2;
+      case5(){
+        <synthetic> val o7: Wrap = A.unapplySeq(x1);
+        if (o7.isEmpty.unary_!)
+          {
+            val xs: Seq[Int] = o7.get.toSeq;
+            matchEnd4(xs)
+          }
+        else
+          case6()
+      };
+      case6(){
+        matchEnd4("other")
+      };
+      matchEnd4(x: Any){
+        x
+      }
+    }
+  }
+}
+
diff --git a/test/files/run/patmat-no-inline-isEmpty.scala b/test/files/run/patmat-no-inline-isEmpty.scala
new file mode 100644
index 000000000000..3af510134c70
--- /dev/null
+++ b/test/files/run/patmat-no-inline-isEmpty.scala
@@ -0,0 +1,31 @@
+import scala.tools.partest._
+
+object Test extends DirectTest {
+  def depCode =
+    """class Wrap(private val a: Int) extends AnyVal {
+      |  def isEmpty: false               = { println("confirm seq isEmpty method doesn't get elided"); false }
+      |  def get                          = this
+      |  def lengthCompare(len: Int)      = Integer.compare(1, len)
+      |  def apply(i: Int)                = if (i == 0) a else Nil(i)
+      |  def drop(n: Int): scala.Seq[Int] = if (n == 0) toSeq else Nil
+      |  def toSeq: scala.Seq[Int]        = List(a)
+      |}
+    """.stripMargin
+
+  override def code =
+    """object A {
+      |  def unapplySeq(a: Int) = new Wrap(a)
+      |}
+      |class T {
+      |  def t: Any = 2 match {
+      |    case A(xs @ _*) => xs
+      |    case _          => "other"
+      |  }
+      |}
+    """.stripMargin
+
+  def show(): Unit = Console.withErr(System.out) {
+    compileString(newCompiler("-usejavacp"))(depCode)
+    compileString(newCompiler("-usejavacp", "-cp", testOutput.path, "-Vprint:patmat"))(code)
+  }
+}
diff --git a/test/files/run/patmat-no-inline-unapply.check b/test/files/run/patmat-no-inline-unapply.check
new file mode 100644
index 000000000000..6b0b6eb2425b
--- /dev/null
+++ b/test/files/run/patmat-no-inline-unapply.check
@@ -0,0 +1,25 @@
+[[syntax trees at end of                    patmat]] // newSource1.scala
+package <empty> {
+  class T extends scala.AnyRef {
+    def <init>(): T = {
+      T.super.<init>();
+      ()
+    };
+    def t: Any = {
+      case <synthetic> val x1: Int(2) = 2;
+      case5(){
+        if (A.unapply(x1))
+          matchEnd4("ok")
+        else
+          case6()
+      };
+      case6(){
+        matchEnd4("other")
+      };
+      matchEnd4(x: Any){
+        x
+      }
+    }
+  }
+}
+
diff --git a/test/files/run/patmat-no-inline-unapply.scala b/test/files/run/patmat-no-inline-unapply.scala
new file mode 100644
index 000000000000..bd6a5541cdd6
--- /dev/null
+++ b/test/files/run/patmat-no-inline-unapply.scala
@@ -0,0 +1,23 @@
+import scala.tools.partest._
+
+object Test extends DirectTest {
+  def depCode =
+    """object A {
+      |  def unapply(a: Int): true = true
+      |}
+    """.stripMargin
+
+  override def code =
+    """class T {
+      |  def t: Any = 2 match {
+      |    case A() => "ok"
+      |    case _   => "other"
+      |  }
+      |}
+    """.stripMargin
+
+  def show(): Unit = Console.withErr(System.out) {
+    compileString(newCompiler("-usejavacp"))(depCode)
+    compileString(newCompiler("-usejavacp", "-cp", testOutput.path, "-Vprint:patmat"))(code)
+  }
+}
diff --git a/test/files/run/patmat-seq.check b/test/files/run/patmat-seq.check
index 8de58f733fb1..ffd4b8c20ac7 100644
--- a/test/files/run/patmat-seq.check
+++ b/test/files/run/patmat-seq.check
@@ -66,7 +66,7 @@ package <empty> {
       case <synthetic> val x1: Int(2) = 2;
       case16(){
         <synthetic> val o18: collection.SeqFactory.UnapplySeqWrapper[Int] = A.unapplySeq(x1);
-        if (false.unary_!)
+        if (o18.isEmpty.unary_!)
           {
             val xs: Seq[Int] = o18.get.toSeq;
             matchEnd15(xs)
@@ -76,7 +76,7 @@ package <empty> {
       };
       case17(){
         <synthetic> val o20: collection.SeqFactory.UnapplySeqWrapper[Int] = A.unapplySeq(x1);
-        if (false.unary_!.&&(o20.get.!=(null).&&(o20.get.lengthCompare(2).==(0))))
+        if (o20.isEmpty.unary_!.&&(o20.get.!=(null).&&(o20.get.lengthCompare(2).==(0))))
           {
             val x: Int = o20.get.apply(0);
             val y: Int = o20.get.apply(1);
@@ -87,7 +87,7 @@ package <empty> {
       };
       case19(){
         <synthetic> val o22: collection.SeqFactory.UnapplySeqWrapper[Int] = A.unapplySeq(x1);
-        if (false.unary_!.&&(o22.get.!=(null).&&(o22.get.lengthCompare(1).>=(0))))
+        if (o22.isEmpty.unary_!.&&(o22.get.!=(null).&&(o22.get.lengthCompare(1).>=(0))))
           {
             val x: Int = o22.get.apply(0);
             val xs: Seq[Int] = o22.get.drop(1);
@@ -267,7 +267,7 @@ package <empty> {
       case <synthetic> val x1: Int(2) = 2;
       case16(){
         <synthetic> val o18: scala.collection.SeqOps = A.unapplySeq(x1);
-        if (false.unary_!())
+        if (scala.collection.SeqFactory.UnapplySeqWrapper.isEmpty$extension(o18).unary_!())
           {
             val xs: Seq = scala.collection.SeqFactory.UnapplySeqWrapper.toSeq$extension(scala.collection.SeqFactory.UnapplySeqWrapper.get$extension(o18));
             matchEnd15(xs)
@@ -277,7 +277,7 @@ package <empty> {
       };
       case17(){
         <synthetic> val o20: scala.collection.SeqOps = A.unapplySeq(x1);
-        if (false.unary_!().&&(new collection.SeqFactory.UnapplySeqWrapper(scala.collection.SeqFactory.UnapplySeqWrapper.get$extension(o20)).!=(null).&&(scala.collection.SeqFactory.UnapplySeqWrapper.lengthCompare$extension(scala.collection.SeqFactory.UnapplySeqWrapper.get$extension(o20), 2).==(0))))
+        if (scala.collection.SeqFactory.UnapplySeqWrapper.isEmpty$extension(o20).unary_!().&&(new collection.SeqFactory.UnapplySeqWrapper(scala.collection.SeqFactory.UnapplySeqWrapper.get$extension(o20)).!=(null).&&(scala.collection.SeqFactory.UnapplySeqWrapper.lengthCompare$extension(scala.collection.SeqFactory.UnapplySeqWrapper.get$extension(o20), 2).==(0))))
           {
             val x: Int = unbox(scala.collection.SeqFactory.UnapplySeqWrapper.apply$extension(scala.collection.SeqFactory.UnapplySeqWrapper.get$extension(o20), 0));
             val y: Int = unbox(scala.collection.SeqFactory.UnapplySeqWrapper.apply$extension(scala.collection.SeqFactory.UnapplySeqWrapper.get$extension(o20), 1));
@@ -288,7 +288,7 @@ package <empty> {
       };
       case19(){
         <synthetic> val o22: scala.collection.SeqOps = A.unapplySeq(x1);
-        if (false.unary_!().&&(new collection.SeqFactory.UnapplySeqWrapper(scala.collection.SeqFactory.UnapplySeqWrapper.get$extension(o22)).!=(null).&&(scala.collection.SeqFactory.UnapplySeqWrapper.lengthCompare$extension(scala.collection.SeqFactory.UnapplySeqWrapper.get$extension(o22), 1).>=(0))))
+        if (scala.collection.SeqFactory.UnapplySeqWrapper.isEmpty$extension(o22).unary_!().&&(new collection.SeqFactory.UnapplySeqWrapper(scala.collection.SeqFactory.UnapplySeqWrapper.get$extension(o22)).!=(null).&&(scala.collection.SeqFactory.UnapplySeqWrapper.lengthCompare$extension(scala.collection.SeqFactory.UnapplySeqWrapper.get$extension(o22), 1).>=(0))))
           {
             val x: Int = unbox(scala.collection.SeqFactory.UnapplySeqWrapper.apply$extension(scala.collection.SeqFactory.UnapplySeqWrapper.get$extension(o22), 0));
             val xs: Seq = scala.collection.SeqFactory.UnapplySeqWrapper.drop$extension(scala.collection.SeqFactory.UnapplySeqWrapper.get$extension(o22), 1);