diff --git a/compiler/btrees.nim b/compiler/btrees.nim
index 5f78c07fe4..d5e7e8099c 100644
--- a/compiler/btrees.nim
+++ b/compiler/btrees.nim
@@ -16,7 +16,7 @@ const
   Mhalf = M div 2
 
 type
-  Node[Key, Val] = ref object
+  Node[Key, Val] {.acyclic.} = ref object
     entries: int
     keys: array[M, Key]
     case isInternal: bool
diff --git a/compiler/ccgtypes.nim b/compiler/ccgtypes.nim
index eb22d79e0d..2fd8156154 100644
--- a/compiler/ccgtypes.nim
+++ b/compiler/ccgtypes.nim
@@ -1327,6 +1327,10 @@ proc genHook(m: BModule; t: PType; info: TLineInfo; op: TTypeAttachedOp): Rope =
 
     genProc(m, theProc)
     result = theProc.loc.r
+
+    when false:
+      if not canFormAcycle(t) and op == attachedTrace:
+        echo "ayclic but has this =trace ", t, " ", theProc.ast
   else:
     when false:
       if op == attachedTrace and m.config.selectedGC == gcOrc and
@@ -1352,9 +1356,12 @@ proc genTypeInfoV2Impl(m: BModule, t, origType: PType, name: Rope; info: TLineIn
   let traceImpl = genHook(m, t, info, attachedTrace)
   let disposeImpl = genHook(m, t, info, attachedDispose)
 
-  addf(m.s[cfsTypeInit3], "$1.destructor = (void*)$2; $1.size = sizeof($3); $1.align = NIM_ALIGNOF($3); $1.name = $4;$n; $1.traceImpl = (void*)$5; $1.disposeImpl = (void*)$6;", [
+  var flags = 0
+  if not canFormAcycle(t): flags = flags or 1
+
+  addf(m.s[cfsTypeInit3], "$1.destructor = (void*)$2; $1.size = sizeof($3); $1.align = NIM_ALIGNOF($3); $1.name = $4;$n; $1.traceImpl = (void*)$5; $1.disposeImpl = (void*)$6; $1.flags = $7;", [
     name, destroyImpl, getTypeDesc(m, t), typeName,
-    traceImpl, disposeImpl])
+    traceImpl, disposeImpl, rope(flags)])
 
   if t.kind == tyObject and t.len > 0 and t[0] != nil and optEnableDeepCopy in m.config.globalOptions:
     discard genTypeInfoV1(m, t, info)
diff --git a/compiler/liftdestructors.nim b/compiler/liftdestructors.nim
index 2948271d9d..c3eee3cfe6 100644
--- a/compiler/liftdestructors.nim
+++ b/compiler/liftdestructors.nim
@@ -468,8 +468,9 @@ proc fillSeqOp(c: var TLiftCtx; t: PType; body, x, y: PNode) =
     forallElements(c, t, body, x, y)
     body.add genBuiltin(c.g, mDestroy, "destroy", x)
   of attachedTrace:
-    # follow all elements:
-    forallElements(c, t, body, x, y)
+    if canFormAcycle(t.elemType):
+      # follow all elements:
+      forallElements(c, t, body, x, y)
   of attachedDispose:
     forallElements(c, t, body, x, y)
     body.add genBuiltin(c.g, mDestroy, "destroy", x)
diff --git a/compiler/semdata.nim b/compiler/semdata.nim
index 13deace0d0..a31c890ec7 100644
--- a/compiler/semdata.nim
+++ b/compiler/semdata.nim
@@ -25,8 +25,8 @@ type
 
   POptionEntry* = ref TOptionEntry
   PProcCon* = ref TProcCon
-  TProcCon* = object          # procedure context; also used for top-level
-                              # statements
+  TProcCon* {.acyclic.} = object # procedure context; also used for top-level
+                                 # statements
     owner*: PSym              # the symbol this context belongs to
     resultSym*: PSym          # the result symbol (if we are in a proc)
     selfSym*: PSym            # the 'self' symbol (if available)
diff --git a/compiler/types.nim b/compiler/types.nim
index de9953e6de..83313550e0 100644
--- a/compiler/types.nim
+++ b/compiler/types.nim
@@ -365,13 +365,13 @@ proc canFormAcycleAux(marker: var IntSet, typ: PType, startId: int): bool =
   if tfAcyclic in t.flags: return
   case t.kind
   of tyTuple, tyObject, tyRef, tySequence, tyArray, tyOpenArray, tyVarargs:
-    if not containsOrIncl(marker, t.id):
+    if t.id == startId:
+      result = true
+    elif not containsOrIncl(marker, t.id):
       for i in 0..<t.len:
         result = canFormAcycleAux(marker, t[i], startId)
         if result: return
       if t.n != nil: result = canFormAcycleNode(marker, t.n, startId)
-    else:
-      result = t.id == startId
     # Inheritance can introduce cyclic types, however this is not relevant
     # as the type that is passed to 'new' is statically known!
     # er but we use it also for the write barrier ...
diff --git a/compiler/vmdef.nim b/compiler/vmdef.nim
index 59ffe95810..9a06d9eb57 100644
--- a/compiler/vmdef.nim
+++ b/compiler/vmdef.nim
@@ -265,7 +265,7 @@ type
     templInstCounter*: ref int # gives every template instantiation a unique ID, needed here for getAst
 
   PStackFrame* = ref TStackFrame
-  TStackFrame* = object
+  TStackFrame* {.acyclic.} = object
     prc*: PSym                 # current prc; proc that is evaluated
     slots*: seq[TFullReg]      # parameters passed to the proc + locals;
                               # parameters come first
diff --git a/lib/system.nim b/lib/system.nim
index 3328b19481..8329bf67f3 100644
--- a/lib/system.nim
+++ b/lib/system.nim
@@ -1754,6 +1754,7 @@ when not defined(js) and defined(nimV2):
       traceImpl: pointer
       disposeImpl: pointer
       typeInfoV1: pointer # for backwards compat, usually nil
+      flags: int
     PNimTypeV2 = ptr TNimTypeV2
 
 when notJSnotNims and defined(nimSeqsV2):
diff --git a/lib/system/orc.nim b/lib/system/orc.nim
index 28f8e58087..c4b1b5c162 100644
--- a/lib/system/orc.nim
+++ b/lib/system/orc.nim
@@ -90,9 +90,21 @@ proc free(s: Cell; desc: PNimTypeV2) {.inline.} =
 
   nimRawDispose(p, desc.align)
 
+template orcAssert(cond, msg) =
+  when logOrc:
+    if not cond:
+      cfprintf(cstderr, "[Bug!] %s\n", msg)
+      quit 1
+
+when logOrc:
+  proc strstr(s, sub: cstring): cstring {.header: "<string.h>", importc.}
+
 proc nimTraceRef(q: pointer; desc: PNimTypeV2; env: pointer) {.compilerRtl, inline.} =
   let p = cast[ptr pointer](q)
   if p[] != nil:
+
+    orcAssert strstr(desc.name, "TType") == nil, "following a TType but it's acyclic!"
+
     var j = cast[ptr GcEnv](env)
     j.traceStack.add(head p[], desc)
 
@@ -102,12 +114,6 @@ proc nimTraceRefDyn(q: pointer; env: pointer) {.compilerRtl, inline.} =
     var j = cast[ptr GcEnv](env)
     j.traceStack.add(head p[], cast[ptr PNimTypeV2](p[])[])
 
-template orcAssert(cond, msg) =
-  when logOrc:
-    if not cond:
-      cfprintf(cstderr, "[Bug!] %s\n", msg)
-      quit 1
-
 var
   roots {.threadvar.}: CellSeq
 
@@ -349,6 +355,8 @@ proc registerCycle(s: Cell; desc: PNimTypeV2) =
     collectCycles()
   #writeCell("[added root]", s)
 
+  orcAssert strstr(desc.name, "TType") == nil, "added a TType as a root!"
+
 proc GC_runOrc* =
   ## Forces a cycle collection pass.
   collectCycles()