diff --git a/compiler/src/dotty/tools/dotc/ast/Desugar.scala b/compiler/src/dotty/tools/dotc/ast/Desugar.scala
index c8b1ed909967..61977be04d1f 100644
--- a/compiler/src/dotty/tools/dotc/ast/Desugar.scala
+++ b/compiler/src/dotty/tools/dotc/ast/Desugar.scala
@@ -142,16 +142,21 @@ object desugar {
     val DefDef(name, tparams, vparamss, tpt, rhs) = meth
     val mods = meth.mods
     val epbuf = new ListBuffer[ValDef]
-    val tparams1 = tparams mapConserve {
-      case tparam @ TypeDef(_, ContextBounds(tbounds, cxbounds)) =>
+    def desugarContextBounds(rhs: Tree): Tree = rhs match {
+      case ContextBounds(tbounds, cxbounds) =>
         for (cxbound <- cxbounds) {
           val paramFlags: FlagSet = if (isPrimaryConstructor) PrivateLocalParamAccessor else Param
           val epname = ctx.freshName(nme.EVIDENCE_PARAM_PREFIX).toTermName
           epbuf += ValDef(epname, cxbound, EmptyTree).withFlags(paramFlags | Implicit)
         }
-        cpy.TypeDef(tparam)(rhs = tbounds)
-      case tparam =>
-        tparam
+        tbounds
+      case PolyTypeTree(tparams, body) =>
+        cpy.PolyTypeTree(rhs)(tparams, desugarContextBounds(body))
+      case _ =>
+        rhs
+    }
+    val tparams1 = tparams mapConserve { tdef =>
+      cpy.TypeDef(tdef)(rhs = desugarContextBounds(tdef.rhs))
     }
 
     val meth1 = addEvidenceParams(cpy.DefDef(meth)(tparams = tparams1), epbuf.toList)
diff --git a/compiler/src/dotty/tools/dotc/core/Denotations.scala b/compiler/src/dotty/tools/dotc/core/Denotations.scala
index 6a39c5787947..99c688d50973 100644
--- a/compiler/src/dotty/tools/dotc/core/Denotations.scala
+++ b/compiler/src/dotty/tools/dotc/core/Denotations.scala
@@ -132,7 +132,7 @@ object Denotations {
     def atSignature(sig: Signature, site: Type = NoPrefix, relaxed: Boolean = false)(implicit ctx: Context): Denotation
 
     /** The variant of this denotation that's current in the given context.
-     *  If no such denotation exists, returns the denotation with each alternative 
+     *  If no such denotation exists, returns the denotation with each alternative
      *  at its first point of definition.
      */
     def current(implicit ctx: Context): Denotation
@@ -744,6 +744,20 @@ object Denotations {
         else NoDenotation
     }
 
+    /** The next defined denotation (following `nextInRun`) or an arbitrary
+     *  undefined denotation, if all denotations in a `nextinRun` cycle are
+     *  undefined.
+     */
+    private def nextDefined: SingleDenotation = {
+      var p1 = this
+      var p2 = nextInRun
+      while (p1.validFor == Nowhere && (p1 ne p2)) {
+        p1 = p1.nextInRun
+        p2 = p2.nextInRun.nextInRun
+      }
+      p1
+    }
+
     /** Produce a denotation that is valid for the given context.
      *  Usually called when !(validFor contains ctx.period)
      *  (even though this is not a precondition).
@@ -763,8 +777,9 @@ object Denotations {
         // can happen if we sit on a stale denotation which has been replaced
         // wholesale by an installAfter; in this case, proceed to the next
         // denotation and try again.
-        if (validFor == Nowhere && nextInRun.validFor != Nowhere) return nextInRun.current
-        assert(false)
+        val nxt = nextDefined
+        if (nxt.validFor != Nowhere) return nxt
+        assert(false, this)
       }
 
       if (valid.runId != currentPeriod.runId)
@@ -905,6 +920,7 @@ object Denotations {
       prev.nextInRun = this
       this.nextInRun = old.nextInRun
       old.validFor = Nowhere
+      old.nextInRun = this
     }
 
     def staleSymbolError(implicit ctx: Context) = {
diff --git a/compiler/src/dotty/tools/dotc/core/Periods.scala b/compiler/src/dotty/tools/dotc/core/Periods.scala
index 6efadab7f271..29d9d208f43c 100644
--- a/compiler/src/dotty/tools/dotc/core/Periods.scala
+++ b/compiler/src/dotty/tools/dotc/core/Periods.scala
@@ -153,7 +153,7 @@ object Periods {
   final val FirstPhaseId = 1
 
   /** The number of bits needed to encode a phase identifier. */
-  final val PhaseWidth = 6
+  final val PhaseWidth = 7
   final val PhaseMask = (1 << PhaseWidth) - 1
   final val MaxPossiblePhaseId = PhaseMask
 }
diff --git a/compiler/src/dotty/tools/dotc/transform/Memoize.scala b/compiler/src/dotty/tools/dotc/transform/Memoize.scala
index 01c240e3ad18..0314d4ec4b10 100644
--- a/compiler/src/dotty/tools/dotc/transform/Memoize.scala
+++ b/compiler/src/dotty/tools/dotc/transform/Memoize.scala
@@ -47,7 +47,9 @@ import Decorators._
     }
     tree match {
       case ddef: DefDef
-        if !ddef.symbol.is(Deferred) && ddef.rhs == EmptyTree =>
+        if !ddef.symbol.is(Deferred) &&
+           !ddef.symbol.isConstructor && // constructors bodies are added later at phase Constructors
+           ddef.rhs == EmptyTree =>
           errorLackImplementation(ddef)
       case tdef: TypeDef
         if tdef.symbol.isClass && !tdef.symbol.is(Deferred) && tdef.rhs == EmptyTree =>
@@ -89,10 +91,10 @@ import Decorators._
     }
 
     lazy val field = sym.field.orElse(newField).asTerm
-    
+
     def adaptToField(tree: Tree) =
       if (tree.isEmpty) tree else tree.ensureConforms(field.info.widen)
-      
+
     if (sym.is(Accessor, butNot = NoFieldNeeded))
       if (sym.isGetter) {
         def skipBlocks(t: Tree): Tree = t match {
diff --git a/tests/pos/i1765.scala b/tests/pos/i1765.scala
new file mode 100644
index 000000000000..d791296381d3
--- /dev/null
+++ b/tests/pos/i1765.scala
@@ -0,0 +1,21 @@
+trait T[X]
+
+trait U[X]
+
+trait TC[M[_]] {
+  def foo[M[_]: TC, A](ma: U[A]) = ()
+  implicit val TCofT: TC[T] = new TC[T] {}
+  implicit def any2T[A](a: A): T[A] = new T[A] {}
+  implicit def any2U[A](a: A): U[A] = new U[A] {}
+  val x = foo[T, Int](1)
+  val y = ()
+}
+
+// Minimized version exhibiting an assertion violation in Denotation#current at phase lambdalift:
+trait TC2 {
+//  implicit val TCofT: TC2[T] = new TC2[T] {}
+  val TCofT: Object = {
+    class C extends TC2
+    new Object
+  }
+}