Index: syneditmarkupifdef.pp
===================================================================
--- syneditmarkupifdef.pp	(revision 44344)
+++ syneditmarkupifdef.pp	(revision 44345)
@@ -1957,18 +1959,22 @@
     //end;
 
     assert(not (PeerList[i].NodeType in [idnIfdef, idnCommentedNode]), 'multi-line peer valid');
-    //if (PeerList[i].NodeType = idnElse) and (AOuterLines <> nil) then begin
+
+    // AOuterLines is only set while scanning opening lines in front of the 1st visible screenline
+    //   (at the start of ValidateRange)
     if (AOuterLines <> nil) then begin
-    // todo: find multiply elseif
-      assert((PeerList[i].NodeType in [idnElse, idnElseIf]), 'multi-line (opening) peer valid');
-      // scanning outer lines
-      j := ToPos(AOuterLines.NodeLineEx[i-1, 1]);
-      if j < 0 then begin
-        //debugln(['Skipping peer for ELSE with NO IFDEF at depth ', i-1, ' before line ', ANode.StartLine]);
-        continue;
-      end;
-      OtherLine := GetOrInsertNodeAtLine(j);
-      MaybeValidateNode(OtherLine);
+      if PeerList[i].NodeType in [idnElse, idnElseIf] then begin
+        // todo: find multiply elseif
+        j := ToPos(AOuterLines.NodeLineEx[i-1, 1]);
+        if j < 0 then begin
+          //debugln(['Skipping peer for ELSE with NO IFDEF at depth ', i-1, ' before line ', ANode.StartLine]);
+          continue;
+        end;
+        OtherLine := GetOrInsertNodeAtLine(j);
+        MaybeValidateNode(OtherLine);
+      end
+      else
+        continue; // while scanning outerlines, any EndIf can be ignored
     end
     else
       OtherLine := ANestList.Node[i]; // Todo: keep if same al last loop, and continue at OtherDepth / j