diff --git a/changelog.txt b/changelog.txt
index 1ed30ae501..30005b7160 100644
--- a/changelog.txt
+++ b/changelog.txt
@@ -33,6 +33,7 @@ Template for new versions:
 ## New Features
 
 ## Fixes
+- `combine`: dyes are combined again, but only when their ``dye_profile`` matches, so mixed dyes no longer revert to a component dye
 - `bodyswap`: fix "invalid argument count" when the target unit has no nemesis record
 - `fix/loyaltycascade`: guard against citizens that are not historical figures and emit a warning.
 - `gui/siegemanager`: fix nil index if there are no siege engines on the map
diff --git a/combine.lua b/combine.lua
index cd9e2522f0..dc10c3789c 100644
--- a/combine.lua
+++ b/combine.lua
@@ -1,3 +1,6 @@
+-- Combine items in stockpiles into stacks.
+--@module = true
+
 local argparse = require('argparse')
 local utils = require('utils')
 
@@ -183,8 +186,6 @@ local function stack_type_new(type_vals)
 end
 
 local function isDye(item)
-    -- Dyes should not be combined as this will cause bugs when mixing them together
-    if item:getType() ~= df.item_type.POWDER_MISC then return false end
     -- pcall guards items/materials that can't be decoded or lack the flag
     local ok, is_dye = pcall(function()
         local mat = dfhack.matinfo.decode(item.mat_type, item.mat_index)
@@ -193,10 +194,30 @@ local function isDye(item)
     return ok and is_dye or false
 end
 
-local function stacks_add_item(stockpile, stacks, stack_type, item, container)
-    -- add an item to the matching comp_items table; based on comp_key.
-    local comp_key = ''
+-- produce a fingerprint of an item's dye_profile, which distinguishes mixed
+-- dyes (e.g. a blend of two dyes) from their components; they all share the
+-- same mat_type/mat_index
+local function dye_profile_key(item)
+    local profile = item.dye_profile
+    -- merchant dyes can lose their profile contents to a vanilla bug (the
+    -- embedded dye_profile is never absent, but has color_index -1); give
+    -- each such dye its own key so they never combine
+    if (not profile or profile.color_index == -1) and isDye(item) then
+        return 'unprofiled+' .. item.id
+    end
+    if not profile then
+        return ''
+    end
+    local parts = {profile.color_index}
+    for _,v in ipairs(profile.dye_material) do parts[#parts+1] = v end
+    for _,v in ipairs(profile.dye_matg) do parts[#parts+1] = v end
+    for _,v in ipairs(profile.degree) do parts[#parts+1] = v end
+    for _,v in ipairs(profile.target_index) do parts[#parts+1] = v end
+    return table.concat(parts, '+')
+end
 
+local function make_comp_key(stack_type, item)
+    local comp_key
     if typesThatUseCreatures[df.item_type[stack_type.type_id]] then
         if not typesThatUseMaterial[df.item_type[stack_type.type_id]] then
             comp_key = ('%s+%s+%s'):format(stack_type.type_id, item.race, item.caste)
@@ -212,6 +233,15 @@ local function stacks_add_item(stockpile, stacks, stack_type, item, container)
     else
         comp_key = ('%s+%s+%s'):format(stack_type.type_id, item.mat_type, item.mat_index)
     end
+    if stack_type.type_id == df.item_type.POWDER_MISC then
+        comp_key = ('%s+%s'):format(comp_key, dye_profile_key(item))
+    end
+    return comp_key
+end
+
+local function stacks_add_item(stockpile, stacks, stack_type, item, container)
+    -- add an item to the matching comp_items table; based on comp_key.
+    local comp_key = make_comp_key(stack_type, item)
 
     if not stack_type.comp_items[comp_key] then
         stack_type.comp_items[comp_key] = comp_item_new(comp_key, stack_type)
@@ -447,7 +477,7 @@ local function stacks_add_items(stockpile, stacks, items, container, ind)
         local stack_type = stacks.stack_types[type_id]
 
         -- item type in list of included types?
-        if stack_type and not item:isSand() and not item:isPlaster() and not isDye(item) and isValidPart(item) then
+        if stack_type and not item:isSand() and not item:isPlaster() and isValidPart(item) then
             if not isRestrictedItem(item) and item.stack_size <= stack_type.max_stack_qty then
 
                 stacks_add_item(stockpile, stacks, stack_type, item, container)
@@ -862,6 +892,13 @@ local function main()
 
 end
 
+if dfhack.internal.IN_TEST then
+    unit_test_hooks = {
+        make_comp_key=make_comp_key,
+        dye_profile_key=dye_profile_key,
+    }
+end
+
 if not dfhack_flags.module then
     main()
 end
diff --git a/test/combine.lua b/test/combine.lua
new file mode 100644
index 0000000000..e12d8f67dc
--- /dev/null
+++ b/test/combine.lua
@@ -0,0 +1,113 @@
+config.target = 'combine'
+
+local combine = reqscript('combine')
+local p = combine.unit_test_hooks
+
+local POWDER_MISC = df.item_type.POWDER_MISC
+local DRINK = df.item_type.DRINK
+
+local function mock_item(item_type, fields)
+    local item = {
+        getType=function() return item_type end,
+        isCrafted=function() return false end,
+    }
+    for k,v in pairs(fields) do item[k] = v end
+    return item
+end
+
+local function mock_dye(color_index, materials)
+    return mock_item(POWDER_MISC, {
+        mat_type=0, mat_index=0,
+        dye_profile={
+            color_index=color_index,
+            dye_material=materials,
+            dye_matg={},
+            degree={},
+            target_index={},
+        },
+    })
+end
+
+function test.dye_same_profile_same_key()
+    local stack_type = {type_id=POWDER_MISC}
+    local dye_a = mock_dye(5, {10})
+    local dye_b = mock_dye(5, {10})
+    expect.eq(p.make_comp_key(stack_type, dye_a),
+              p.make_comp_key(stack_type, dye_b))
+end
+
+function test.dye_different_color_different_key()
+    local stack_type = {type_id=POWDER_MISC}
+    local dye_a = mock_dye(5, {10})
+    local dye_b = mock_dye(7, {10})
+    expect.ne(p.make_comp_key(stack_type, dye_a),
+              p.make_comp_key(stack_type, dye_b))
+end
+
+function test.dye_mix_different_key_than_component()
+    -- a mixed dye shares mat_type/mat_index with its components but has a
+    -- different dye_profile; it must not be merged into a component stack
+    local stack_type = {type_id=POWDER_MISC}
+    local dye_a = mock_dye(5, {10})
+    local dye_mix = mock_dye(5, {10, 20})
+    expect.ne(p.make_comp_key(stack_type, dye_a),
+              p.make_comp_key(stack_type, dye_mix))
+end
+
+function test.powder_without_profile()
+    -- non-dye powders have an empty/unset profile and still merge as before
+    local stack_type = {type_id=POWDER_MISC}
+    local p1 = mock_item(POWDER_MISC, {mat_type=1, mat_index=2})
+    local p2 = mock_item(POWDER_MISC, {mat_type=1, mat_index=2})
+    expect.eq(p.make_comp_key(stack_type, p1),
+              p.make_comp_key(stack_type, p2))
+end
+
+local function find_dye_mat()
+    for _, plant in ipairs(df.global.world.raws.plants.all) do
+        local mtype = plant.material_defs.type.mill
+        local midx = plant.material_defs.idx.mill
+        if mtype ~= -1 then
+            local matinfo = dfhack.matinfo.decode(mtype, midx)
+            if matinfo and matinfo.material.flags.IS_DYE then
+                return mtype, midx
+            end
+        end
+    end
+end
+
+function test.unprofiled_dye_never_combines()
+    -- merchant dyes can lose their dye_profile to a vanilla bug; such items
+    -- must not be merged, not even with each other. on real items the
+    -- embedded dye_profile is never absent but has color_index -1
+    local mtype, midx = find_dye_mat()
+    if not mtype then return end
+    local empty_profile = {color_index=-1, dye_material={}, dye_matg={},
+                           degree={}, target_index={}}
+    local stack_type = {type_id=POWDER_MISC}
+    local d1 = mock_item(POWDER_MISC, {mat_type=mtype, mat_index=midx, id=101,
+                                     dye_profile=empty_profile})
+    local d2 = mock_item(POWDER_MISC, {mat_type=mtype, mat_index=midx, id=102,
+                                     dye_profile=empty_profile})
+    local d3 = mock_item(POWDER_MISC, {mat_type=mtype, mat_index=midx, id=103})
+    local d4 = mock_item(POWDER_MISC, {mat_type=mtype, mat_index=midx, id=104,
+        dye_profile={color_index=1, dye_material={1}, dye_matg={}, degree={},
+                     target_index={}}})
+    expect.ne(p.make_comp_key(stack_type, d1),
+              p.make_comp_key(stack_type, d2))
+    expect.ne(p.make_comp_key(stack_type, d1),
+              p.make_comp_key(stack_type, d3))
+    expect.ne(p.make_comp_key(stack_type, d1),
+              p.make_comp_key(stack_type, d4))
+end
+
+function test.dye_key_ignores_other_types()
+    local stack_type = {type_id=DRINK}
+    local d1 = mock_item(DRINK, {mat_type=1, mat_index=2})
+    local d2 = mock_item(DRINK, {mat_type=1, mat_index=2,
+                               dye_profile={color_index=9, dye_material={1},
+                                            dye_matg={}, degree={},
+                                            target_index={}}})
+    expect.eq(p.make_comp_key(stack_type, d1),
+              p.make_comp_key(stack_type, d2))
+end