diff --git a/components/esm/loadmgef.cpp b/components/esm/loadmgef.cpp
index f60191539..04d55c828 100644
--- a/components/esm/loadmgef.cpp
+++ b/components/esm/loadmgef.cpp
@@ -42,8 +42,13 @@ void MagicEffect::load(ESMReader &esm)
   esm.getHNT(mIndex, "INDX");
 
   esm.getHNT(mData, "MEDT", 36);
-  if (mIndex>=0 && mIndex<NumberOfHardcodedFlags)
-    mData.mFlags |= HardcodedFlags[mIndex];
+  if (esm.getFormat() == 0)
+  {
+      // don't allow mods to change fixed flags in the legacy format
+      mData.mFlags &= (AllowSpellmaking | AllowEnchanting | NegativeLight);
+      if (mIndex>=0 && mIndex<NumberOfHardcodedFlags)
+        mData.mFlags |= HardcodedFlags[mIndex];
+  }
 
   mIcon = esm.getHNOString("ITEX");
   mParticle = esm.getHNOString("PTEX");
diff --git a/components/esm/loadmgef.hpp b/components/esm/loadmgef.hpp
index 64835530c..568cbe283 100644
--- a/components/esm/loadmgef.hpp
+++ b/components/esm/loadmgef.hpp
@@ -16,7 +16,7 @@ struct MagicEffect
 
     enum Flags
     {
-        // Hardcoded flags
+        // Originally fixed flags (HardcodedFlags array consists of just these)
         TargetSkill = 0x1, // Affects a specific skill, which is specified elsewhere in the effect structure.
         TargetAttribute = 0x2, // Affects a specific attribute, which is specified elsewhere in the effect structure.
         NoDuration = 0x4, // Has no duration. Only runs effect once on cast.
@@ -31,11 +31,12 @@ struct MagicEffect
         Unreflectable = 0x10000, // Cannot be reflected, the effect always lands normally.
         CasterLinked = 0x20000,	// Must quench if caster is dead, or not an NPC/creature. Not allowed in containter/door trap spells.
 
-        // Moddable flags
-        AllowSpellmaking = 0x200,
-        AllowEnchanting = 0x400,
-        Negative = 0x800 // TODO: needs research
+        // Originally modifiable flags
+        AllowSpellmaking = 0x200, // Can be used for spellmaking
+        AllowEnchanting = 0x400, // Can be used for enchanting
+        NegativeLight = 0x800 // Negative light source
     };
+
     enum MagnitudeDisplayType
     {
         MDT_None,