diff --git a/api/api.lua b/api/api.lua
index 2d70f34d..74d4904b 100644
--- a/api/api.lua
+++ b/api/api.lua
@@ -1277,7 +1277,7 @@ end
 -- 'barsize'    integer number of buttons,
 -- 'formfactor' string formfactor in cols x rows,
 -- 'padding'    the spacing between buttons
-function pfUI.api.BarLayoutSize(bar,barsize,formfactor,iconsize,bordersize,padding,uneven)
+function pfUI.api.BarLayoutSize(bar,barsize,formfactor,iconsize,bordersize,padding,uneven,fillmode)
   assert(barsize > 0 and barsize <= NUM_ACTIONBAR_BUTTONS,"BarLayoutSize: barsize "..tostring(barsize).." is invalid")
   local cols, rows = ResolveBarLayout(barsize, formfactor, uneven)
   if not cols or not rows then cols, rows = unpack(pfGridmath[barsize][1]) end
@@ -1295,21 +1295,53 @@ end
 -- 'iconsize'     size of the button
 -- 'bordersize'   default bordersize
 -- 'padding'      the spacing between buttons
-function pfUI.api.BarButtonAnchor(button,basename,buttonindex,barsize,formfactor,iconsize,bordersize,padding,uneven)
+function pfUI.api.BarButtonAnchor(button,basename,buttonindex,barsize,formfactor,iconsize,bordersize,padding,uneven,fillmode)
   assert(barsize > 0 and barsize <= NUM_ACTIONBAR_BUTTONS,"BarButtonAnchor: barsize "..tostring(barsize).." is invalid")
   local cols, rows, mode, orientation = ResolveBarLayout(barsize, formfactor, uneven)
   if not cols or not rows then
     cols, rows, mode, orientation = unpack(pfGridmath[barsize][1]), "rows", "DOWN"
   end
+
+  -- fillmode: remap buttonindex to slotindex (grid position in native fill order)
+  -- only needed when fill direction differs from layout mode
+  local slotindex = buttonindex
+  if fillmode == "row" and mode == "cols" then
+    local full = math.floor(barsize / rows)
+    local rem = barsize - full * rows
+    local n = 0
+    for r = 1, rows do
+      local w = full + ((r <= rem) and 1 or 0)
+      if n + w >= buttonindex then
+        local c = buttonindex - n
+        slotindex = (c - 1) * rows + r
+        break
+      end
+      n = n + w
+    end
+  elseif fillmode == "col" and mode == "rows" then
+    local full = math.floor(barsize / cols)
+    local rem = barsize - full * cols
+    local n = 0
+    for c = 1, cols do
+      local h = full + ((c <= rem) and 1 or 0)
+      if n + h >= buttonindex then
+        local r = buttonindex - n
+        slotindex = (r - 1) * cols + c
+        break
+      end
+      n = n + h
+    end
+  end
+
   local parent = button:GetParent()
   local step = iconsize + bordersize*2 + padding
   local row, col
   if mode == "cols" then
-    col = math.ceil(buttonindex / rows)
-    row = buttonindex - ((col-1) * rows)
+    col = math.ceil(slotindex / rows)
+    row = slotindex - ((col-1) * rows)
   else
-    row = math.ceil(buttonindex / cols)
-    col = buttonindex - ((row-1) * cols)
+    row = math.ceil(slotindex / cols)
+    col = slotindex - ((row-1) * cols)
   end
   if mode == "cols" and orientation == "LEFT" then
     local final_col = math.ceil(barsize / rows)
@@ -1326,7 +1358,7 @@ function pfUI.api.BarButtonAnchor(button,basename,buttonindex,barsize,formfactor
   end
   local x = bordersize + padding + (col - 1) * step
   local y = -bordersize - padding - (row - 1) * step
-  if buttonindex == 1 then
+  if slotindex == 1 then
     button._anchor = {"TOPLEFT", parent, "TOPLEFT", x, y}
   else
     button._anchor = {"TOPLEFT", parent, "TOPLEFT", x, y}
diff --git a/modules/actionbar.lua b/modules/actionbar.lua
index 7656e130..2e10f490 100644
--- a/modules/actionbar.lua
+++ b/modules/actionbar.lua
@@ -1277,6 +1277,7 @@ pfUI:RegisterModule("actionbar", "vanilla", function ()
     local background = C.bars["bar"..i].background
     local formfactor = C.bars["bar"..i].formfactor
     local uneven = C.bars["bar"..i].uneven or "Down"
+    local fillmode = C.bars["bar"..i].fillmode or "auto"
     -- validate uneven against bar shape and reset if incompatible
     local _, _, fcols2, frows2 = string.find(tostring(formfactor or ""), "(%d+)%s*x%s*(%d+)")
     fcols2, frows2 = tonumber(fcols2), tonumber(frows2)
@@ -1421,7 +1422,7 @@ pfUI:RegisterModule("actionbar", "vanilla", function ()
       bars[i][j] = CreateActionButton(bars[i], i, j)
       bars[i][j].bar = i
 
-      BarButtonAnchor(bars[i][j], buttonbasename, j, buttons, formfactor, size, border, spacing, uneven)
+      BarButtonAnchor(bars[i][j], buttonbasename, j, buttons, formfactor, size, border, spacing, uneven, fillmode)
       bars[i][j]:ClearAllPoints()
       bars[i][j]:SetPoint(unpack(bars[i][j]._anchor))
       bars[i][j]:Show()
@@ -1452,7 +1453,7 @@ pfUI:RegisterModule("actionbar", "vanilla", function ()
     end
 
     -- adjust actionbar size
-    BarLayoutSize(bars[i], buttons, formfactor, size, border, spacing, uneven)
+    BarLayoutSize(bars[i], buttons, formfactor, size, border, spacing, uneven, fillmode)
     bars[i]:SetWidth(bars[i]._size[1])
     bars[i]:SetHeight(bars[i]._size[2])
     bars[i]:ClearAllPoints()
diff --git a/modules/gui.lua b/modules/gui.lua
index 8a930355..4186e2bb 100644
--- a/modules/gui.lua
+++ b/modules/gui.lua
@@ -2662,6 +2662,9 @@ pfUI:RegisterModule("gui", "vanilla:tbc", function ()
         end
         CreateConfig(layout_ufunc, T["Layout"], C.bars["bar"..id], "formfactor", "dropdown", formfactors)
         uneven_frame = CreateConfig(U["bars"], T["Layout Uneven Orientation"], C.bars["bar"..id], "uneven", "dropdown", uneven_options)
+        CreateConfig(U["bars"], T["Fill Order"], C.bars["bar"..id], "fillmode", "dropdown", function()
+          return {"auto:Auto", "row:Row-first (1,2,3 / 4,5,6)", "col:Column-first (1,3,5 / 2,4,6)"}
+        end)
         CreateConfig(U["bars"], T["Bar Background"], C.bars["bar"..id], "background", "checkbox")
         CreateConfig(U["bars"], T["Show Hotkey Text"], C.bars["bar"..id], "showkeybind", "checkbox")