diff --git a/polymer/eduke32/source/lunatic/con_lang.lua b/polymer/eduke32/source/lunatic/con_lang.lua
index c819b4a99..74b65195f 100644
--- a/polymer/eduke32/source/lunatic/con_lang.lua
+++ b/polymer/eduke32/source/lunatic/con_lang.lua
@@ -754,6 +754,22 @@ StructAccessCode =
     player = PlayerLabels,
 }
 
+local function tonegtag(LabelsTab, member, funcname)
+    local memb = LabelsTab[member]
+    LabelsTab[member] = { memb, memb.."="..funcname.."(%%s)" }
+end
+
+function setup_negative_tag_check(funcname)
+    tonegtag(TspriteLabels, "tsprlotag", funcname)
+    tonegtag(TspriteLabels, "tsprhitag", funcname)
+    tonegtag(ActorLabels, "lotag", funcname)
+    tonegtag(ActorLabels, "hitag", funcname)
+    tonegtag(WallLabels, "lotag", funcname)
+    tonegtag(WallLabels, "hitag", funcname)
+    tonegtag(SectorLabels, "lotag", funcname)
+    tonegtag(SectorLabels, "hitag", funcname)
+end
+
 local PROJ = function(memb) return "projectile[%s]"..memb end
 local THISPROJ = function(memb) return "actor[%s].proj"..memb end
 
diff --git a/polymer/eduke32/source/lunatic/control.lua b/polymer/eduke32/source/lunatic/control.lua
index 4b2f8fa83..cf14c7419 100644
--- a/polymer/eduke32/source/lunatic/control.lua
+++ b/polymer/eduke32/source/lunatic/control.lua
@@ -528,6 +528,13 @@ function _get_userdef(pli)
     return ffiC.ud
 end
 
+function _err_if_negative(val)
+    if (not (val >= 0)) then
+        error("setting tag to negative value", 2)
+    end
+    return val
+end
+
 --- player/actor/sprite searching functions ---
 
 local xmath = require("xmath")
diff --git a/polymer/eduke32/source/lunatic/doc/lunacon.txt b/polymer/eduke32/source/lunatic/doc/lunacon.txt
index feda13f01..9ae7a4147 100644
--- a/polymer/eduke32/source/lunatic/doc/lunacon.txt
+++ b/polymer/eduke32/source/lunatic/doc/lunacon.txt
@@ -181,6 +181,16 @@ If enabled, an attept to issue `getuserdef` or `setuserdef` when the current
 player doesn't equal the local player generates an error. Otherwise, the
 userdef structure can be accessed irrespective of the current player.
 
+`-ferror-negative-tag-write` (default: off)::
+If enabled, an attempt to assign a negative value to the `lotag` or `hitag`
+member of the sector, wall or (t)sprite structures produces an error.
+Normally, it is legal to assign negative values to these members, but since
+they are unsigned 16-bit integers on the C side, such values will be converted
+to positive ones and may entail undesired behavior.
++
+NOTE: From CON as well as Lunatic, `hitag` and `lotag` are seen as *signed*
+16-bit integers.
+
 `-fbad-getactorvar-use-pli` (default: off)::
 If enabled and `-Werror-bad-getactorvar` is off, a `getactorvar` of a
 per-player variable will result the gamevar being indexed with the current
diff --git a/polymer/eduke32/source/lunatic/lunacon.lua b/polymer/eduke32/source/lunatic/lunacon.lua
index ef296475f..c63dd286c 100644
--- a/polymer/eduke32/source/lunatic/lunacon.lua
+++ b/polymer/eduke32/source/lunatic/lunacon.lua
@@ -127,7 +127,8 @@ local g_cgopt = { ["no"]=false, ["debug-lineinfo"]=false, ["gendir"]=nil,
                   ["cache-sap"]=false, ["error-nostate"]=true,
                   ["playervar"]=true, ["trapv"]=false, ["wrapv"]=false,
                   ["bad-getactorvar-use-pli"]=false,
-                  ["error-nonlocal-userdef"]=true, }
+                  ["error-nonlocal-userdef"]=true,
+                  ["error-negative-tag-write"]=false, }
 
 local function csapp() return g_cgopt["cache-sap"] end
 
@@ -230,6 +231,10 @@ else
     end
 end
 
+if (g_cgopt["error-negative-tag-write"]) then
+    conl.setup_negative_tag_check("_st")
+end
+
 -- Stack with *true* on top if the innermost block is a "whilevar*n".
 local g_isWhile = {}
 -- Sequence number of 'while' statements, used to implement CON "break" inside
@@ -309,6 +314,7 @@ local function new_initial_codetab()
         "local _setsprite,_ssp = _con._setsprite,_con._ssp",
         g_cgopt["error-nonlocal-userdef"]
             and "local _gud=_con._get_userdef_check" or "local _gud=_con._get_userdef",
+        "local _st=_con._err_if_negative",
 
         -- * CON "states" (subroutines) and
         -- * Switch function table, indexed by global switch sequence number: