diff --git a/tools/build-pkg.lua b/tools/build-pkg.lua
index 7a7172f9..a78c4442 100755
--- a/tools/build-pkg.lua
+++ b/tools/build-pkg.lua
@@ -548,6 +548,57 @@ local function removeEmptyDirs(item)
     end
 end
 
+local function prepareTree(pass, item, item2deps, prev_files, item2index)
+    if pass == 'first' then
+        gitCheckout(
+            itemToBranch(item, pass),
+            item2deps[item],
+            item2index,
+            pass
+        )
+    elseif pass == 'second' then
+        -- Build item second time to check if it builds correctly if
+        -- its followers and unrelated packages have been built.
+        gitCheckout(
+            itemToBranch(item, 'second'),
+            {GIT_ALL_PSEUDOITEM},
+            item2index,
+            'first'
+        )
+        -- Remove files of item from previous build.
+        for _, file in ipairs(prev_files) do
+            os.remove(file)
+        end
+        removeEmptyDirs()
+        gitAdd()
+        gitCommit(("Remove %s to rebuild it"):format(item, pass))
+    else
+        error("Unknown pass: " .. pass)
+    end
+end
+
+local function comparePasses(item, new_files, prev_file2item, prev_files)
+    local files_set = {}
+    for _, file in ipairs(new_files) do
+        if not prev_file2item[file] then
+            log('Item %s installs a file on second pass only: %s',
+                item, file)
+        elseif prev_file2item[file] ~= item then
+            log('File %s was installed by %s on first pass ' ..
+                'and by %s - on the second pass',
+                file, prev_file2item[file], item)
+        end
+        files_set[file] = true
+    end
+    for _, file in ipairs(prev_files) do
+        if not files_set[file] then
+            log('Item %s installs a file on first pass only: %s',
+                item, file)
+        end
+    end
+    -- TODO compare contents of files (nm for binaries)
+end
+
 local function isBuilt(item, files)
     local target, pkg = parseItem(item)
     local INSTALLED = 'usr/%s/installed/%s'
@@ -561,10 +612,9 @@ local function isBuilt(item, files)
 end
 
 -- builds package, returns list of new files
-local function buildItem(item, item2deps, file2item, item2index, pass)
-    gitCheckout(
-        itemToBranch(item, pass), item2deps[item], item2index, pass
-    )
+-- prev_files is passed only to second pass.
+local function buildItem(item, item2deps, file2item, item2index, pass, prev_files)
+    prepareTree(pass, item, item2deps, prev_files, item2index)
     local target, pkg = parseItem(item)
     local cmd = '%s %s MXE_TARGETS=%s --jobs=1'
     os.execute(cmd:format(tool 'make', pkg, target))
@@ -573,9 +623,13 @@ local function buildItem(item, item2deps, file2item, item2index, pass)
     if #new_files + #changed_files > 0 then
         gitCommit(("Build %s, pass %s"):format(item, pass))
     end
-    for _, file in ipairs(new_files) do
-        checkFile(file, item)
-        file2item[file] = item
+    if pass == 'first' then
+        for _, file in ipairs(new_files) do
+            checkFile(file, item)
+            file2item[file] = item
+        end
+    elseif isBuilt(item, new_files) then
+        comparePasses(item, new_files, file2item, prev_files)
     end
     for _, file in ipairs(changed_files) do
         checkFile(file, item)
@@ -776,7 +830,8 @@ local function isEmpty(files)
 end
 
 -- build all packages, save filelist to list file
-local function buildPackages(items, item2deps, pass)
+-- prev_files is passed only to second pass.
+local function buildPackages(items, item2deps, pass, prev_item2files)
     local broken = {}
     local unbroken = {}
     local file2item = {}
@@ -789,12 +844,22 @@ local function buildPackages(items, item2deps, pass)
         end
         return false
     end
+    if pass == 'second' then
+        assert(prev_item2files)
+        -- fill file2item with data from prev_item2files
+        for item, files in pairs(prev_item2files) do
+            for _, file in ipairs(files) do
+                file2item[file] = item
+            end
+        end
+    end
     local item2index = makeItem2Index(items)
     local progress_printer = progressPrinter(items)
     for i, item in ipairs(items) do
         if not brokenDep(item) then
+            local prev_files = prev_item2files and prev_item2files[item]
             local files = buildItem(
-                item, item2deps, file2item, item2index, pass
+                item, item2deps, file2item, item2index, pass, prev_files
             )
             findForeignInstalls(item, files)
             if isBuilt(item, files) then
@@ -959,6 +1024,10 @@ local function main()
         makeMxeRequirementsPackage('jessie')
     end
     makeMxeSourcePackage()
+    -- second pass
+    buildPackages(
+        build_list, item2deps, 'second', item2files
+    )
     if #unbroken < #build_list then
         local code = 1
         local close = true