diff --git a/compiler/src/dotty/tools/dotc/parsing/Parsers.scala b/compiler/src/dotty/tools/dotc/parsing/Parsers.scala
index 2436ad4081f2..d21d991f65ee 100644
--- a/compiler/src/dotty/tools/dotc/parsing/Parsers.scala
+++ b/compiler/src/dotty/tools/dotc/parsing/Parsers.scala
@@ -1564,7 +1564,6 @@ object Parsers {
      *                    |  `(' [Patterns] `)'
      *                    |  SimplePattern1 [TypeArgs] [ArgumentPatterns]
      *  SimplePattern1   ::= Path
-     *                    |  `{' Block `}'
      *                    |  SimplePattern1 `.' id
      *  PatVar           ::= id
      *                    |  `_'
@@ -1587,8 +1586,6 @@ object Parsers {
         } else wildIndent
       case LPAREN =>
         atPos(in.offset) { makeTupleOrParens(inParens(patternsOpt())) }
-      case LBRACE =>
-        dotSelectors(blockExpr())
       case XMLSTART =>
         xmlLiteralPattern()
       case _ =>
diff --git a/compiler/src/dotty/tools/dotc/typer/ReTyper.scala b/compiler/src/dotty/tools/dotc/typer/ReTyper.scala
index 7031b7920f2a..b5ca1c651443 100644
--- a/compiler/src/dotty/tools/dotc/typer/ReTyper.scala
+++ b/compiler/src/dotty/tools/dotc/typer/ReTyper.scala
@@ -35,7 +35,8 @@ class ReTyper extends Typer {
 
   override def typedSelect(tree: untpd.Select, pt: Type)(implicit ctx: Context): Tree = {
     assert(tree.hasType, tree)
-    val qual1 = typed(tree.qualifier, AnySelectionProto)
+    // a qualifier cannot be a pattern
+    val qual1 = typed(tree.qualifier, AnySelectionProto)(ctx.retractMode(Mode.Pattern))
     untpd.cpy.Select(tree)(qual1, tree.name).withType(tree.typeOpt)
   }
 
diff --git a/compiler/src/dotty/tools/dotc/typer/Typer.scala b/compiler/src/dotty/tools/dotc/typer/Typer.scala
index 20d7369bf11f..ff40b4a61a5a 100644
--- a/compiler/src/dotty/tools/dotc/typer/Typer.scala
+++ b/compiler/src/dotty/tools/dotc/typer/Typer.scala
@@ -406,9 +406,23 @@ class Typer extends Namer
         tree.withType(ownType)
     }
 
+    checkStableIdentPattern(tree1, pt)
     checkValue(tree1, pt)
   }
 
+  /** Check that a stable identifier pattern is indeed stable (SLS 8.1.5)
+   */
+  private def checkStableIdentPattern(tree: Tree, pt: Type)(implicit ctx: Context): Tree = {
+    if (ctx.mode.is(Mode.Pattern) &&
+        !tree.isType &&
+        !pt.isInstanceOf[ApplyingProto] &&
+        !tree.tpe.isStable &&
+        !isWildcardArg(tree))
+      ctx.error(s"stable identifier required, but ${tree.show} found", tree.pos)
+
+    tree
+  }
+
   private def typedSelect(tree: untpd.Select, pt: Type, qual: Tree)(implicit ctx: Context): Select =
     checkValue(assignType(cpy.Select(tree)(qual, tree.name), qual), pt)
 
@@ -418,7 +432,7 @@ class Typer extends Namer
       val qual1 = typedExpr(tree.qualifier, selectionProto(tree.name, pt, this))
       if (tree.name.isTypeName) checkStable(qual1.tpe, qual1.pos)
       val select = typedSelect(tree, pt, qual1)
-      if (select.tpe ne TryDynamicCallType) select
+      if (select.tpe ne TryDynamicCallType) checkStableIdentPattern(select, pt)
       else if (pt.isInstanceOf[PolyProto] || pt.isInstanceOf[FunProto] || pt == AssignProto) select
       else typedDynamicSelect(tree, Nil, pt)
     }
diff --git a/docs/docs/internals/syntax.md b/docs/docs/internals/syntax.md
index ddc70855ff1d..40825d221589 100644
--- a/docs/docs/internals/syntax.md
+++ b/docs/docs/internals/syntax.md
@@ -202,7 +202,7 @@ ParArgumentExprs  ::=  ‘(’ ExprsInParens ‘)’
                     |  ‘(’ [ExprsInParens] PostfixExpr ‘:’ ‘_’ ‘*’ ‘)’          exprs :+ Typed(expr, Ident(wildcardStar))
 ArgumentExprs     ::=  ParArgumentExprs
                     |  [nl] BlockExpr
-BlockExpr         ::=  ‘{’ BlockExprContents ‘}’                                
+BlockExpr         ::=  ‘{’ BlockExprContents ‘}’
 BlockExprContents ::=  CaseClauses | Block
 Block             ::=  {BlockStat semi} [BlockResult]                           Block(stats, expr?)
 BlockStat         ::=  Import
@@ -234,7 +234,6 @@ SimplePattern     ::=  PatVar
                     |  XmlPattern
                     |  SimplePattern1 [TypeArgs] [ArgumentPatterns]
 SimplePattern1    ::=  Path
-                    |  ‘{’ Block ‘}’
                     |  SimplePattern1 ‘.’ id
 PatVar            ::=  varid
                     |  ‘_’
diff --git a/tests/neg/i1846.scala b/tests/neg/i1846.scala
new file mode 100644
index 000000000000..f661a86d5daf
--- /dev/null
+++ b/tests/neg/i1846.scala
@@ -0,0 +1,19 @@
+object Test {
+  def main(args: Array[String]): Unit = {
+    val x = 42
+    val Y = "42"
+
+    x match { case { 42 }           => () } // error
+    x match { case { 42.toString }  => () } // error
+    x match { case { 42 }.toString  => () } // error
+    x match { case "42".toInt       => () } // error
+    x match { case { "42".toInt }   => () } // error
+    x match { case { "42" }.toInt   => () } // error
+    x match { case { "42".toInt }   => () } // error
+    x match { case Y                => () } // error
+    x match { case { Y.toInt }      => () } // error
+    x match { case { Y }.toInt      => () } // error
+    x match { case { Y }.toString   => () } // error
+    x match { case { Y.toString }   => () } // error
+  }
+}
diff --git a/tests/neg/i3812.scala b/tests/neg/i3812.scala
new file mode 100644
index 000000000000..182721d65ea0
--- /dev/null
+++ b/tests/neg/i3812.scala
@@ -0,0 +1,13 @@
+object Test {
+  def main(args: Array[String]): Unit = {
+    val x = 42
+    val Y = "42"
+
+    x match { case { 42 }           => () } // error
+    x match { case { "42".toInt }   => () } // error
+    x match { case { "42" }.toInt   => () } // error
+    x match { case { "42".toInt }   => () } // error
+    x match { case { Y.toInt }      => () } // error
+    x match { case { Y }.toInt      => () } // error
+  }
+}
diff --git a/tests/neg/i3812b.scala b/tests/neg/i3812b.scala
new file mode 100644
index 000000000000..e9b0c291ef3f
--- /dev/null
+++ b/tests/neg/i3812b.scala
@@ -0,0 +1,27 @@
+object Test {
+  def main(args: Array[String]): Unit = {
+    case class Box(v: Int)
+
+    val x = 42
+    var Y1 = 42
+    val Y2 = "42"
+    var Z1 = Box(4)
+    val Z2 = Box(4)
+
+    x match { case Y1                => () } // error
+    x match { case Y2.toInt          => () } // error
+    x match { case Y1.toString       => () } // error
+
+    x match { case Z1.v              => () } // error
+    x match { case Z2.v              => () } // ok
+
+    Some(x) match { case Some(Z1.v)  => () } // error
+    Some(x) match { case Some(Z2.v)  => () } // ok
+
+    Some(x) match { case Some(4) | Some(Z1.v) => () } // error
+    Some(x) match { case a @ Some(Z1.v)       => () } // error
+
+    Some(x) match { case Some(4) | Some(Z2.v) => () } // ok
+    Some(x) match { case a @ Some(Z2.v)       => () } // ok
+  }
+}