diff --git a/tools/releasetools/blockimgdiff.py b/tools/releasetools/blockimgdiff.py
index be5b32a..24c5b2d 100644
--- a/tools/releasetools/blockimgdiff.py
+++ b/tools/releasetools/blockimgdiff.py
@@ -272,6 +272,7 @@
   # Reasons for not applying imgdiff on APKs.
   SKIPPED_TRIMMED = "Not used imgdiff due to trimmed RangeSet"
   SKIPPED_NONMONOTONIC = "Not used imgdiff due to having non-monotonic ranges"
+  SKIPPED_SHARED_BLOCKS = "Not used imgdiff due to using shared blocks"
   SKIPPED_INCOMPLETE = "Not used imgdiff due to incomplete RangeSet"
 
   # The list of valid reasons, which will also be the dumped order in a report.
@@ -280,6 +281,7 @@
       USED_IMGDIFF_LARGE_APK,
       SKIPPED_TRIMMED,
       SKIPPED_NONMONOTONIC,
+      SKIPPED_SHARED_BLOCKS,
       SKIPPED_INCOMPLETE,
   )
 
@@ -414,6 +416,7 @@
       - The file type is supported by imgdiff;
       - The source and target blocks are monotonic (i.e. the data is stored with
         blocks in increasing order);
+      - Both files don't contain shared blocks;
       - Both files have complete lists of blocks;
       - We haven't removed any blocks from the source set.
 
@@ -437,6 +440,11 @@
       self.imgdiff_stats.Log(name, ImgdiffStats.SKIPPED_NONMONOTONIC)
       return False
 
+    if (tgt_ranges.extra.get('uses_shared_blocks') or
+        src_ranges.extra.get('uses_shared_blocks')):
+      self.imgdiff_stats.Log(name, ImgdiffStats.SKIPPED_SHARED_BLOCKS)
+      return False
+
     if tgt_ranges.extra.get('incomplete') or src_ranges.extra.get('incomplete'):
       self.imgdiff_stats.Log(name, ImgdiffStats.SKIPPED_INCOMPLETE)
       return False
diff --git a/tools/releasetools/common.py b/tools/releasetools/common.py
index 16600ed..370710e 100644
--- a/tools/releasetools/common.py
+++ b/tools/releasetools/common.py
@@ -625,7 +625,7 @@
   return tmp, zipfile.ZipFile(filename, "r")
 
 
-def GetSparseImage(which, tmpdir, input_zip):
+def GetSparseImage(which, tmpdir, input_zip, allow_shared_blocks):
   """Returns a SparseImage object suitable for passing to BlockImageDiff.
 
   This function loads the specified sparse image from the given path, and
@@ -637,6 +637,7 @@
     which: The partition name, which must be "system" or "vendor".
     tmpdir: The directory that contains the prebuilt image and block map file.
     input_zip: The target-files ZIP archive.
+    allow_shared_blocks: Whether having shared blocks is allowed.
 
   Returns:
     A SparseImage object, with file_map info loaded.
@@ -655,7 +656,8 @@
   # unconditionally. Note that they are still part of care_map. (Bug: 20939131)
   clobbered_blocks = "0"
 
-  image = sparse_img.SparseImage(path, mappath, clobbered_blocks)
+  image = sparse_img.SparseImage(path, mappath, clobbered_blocks,
+                                 allow_shared_blocks=allow_shared_blocks)
 
   # block.map may contain less blocks, because mke2fs may skip allocating blocks
   # if they contain all zeros. We can't reconstruct such a file from its block
@@ -669,6 +671,13 @@
 
     info = input_zip.getinfo(arcname)
     ranges = image.file_map[entry]
+
+    # If a RangeSet has been tagged as using shared blocks while loading the
+    # image, its block list must be already incomplete due to that reason. Don't
+    # give it 'incomplete' tag to avoid messing up the imgdiff stats.
+    if ranges.extra.get('uses_shared_blocks'):
+      continue
+
     if RoundUpTo4K(info.file_size) > ranges.size() * 4096:
       ranges.extra['incomplete'] = True
 
diff --git a/tools/releasetools/ota_from_target_files.py b/tools/releasetools/ota_from_target_files.py
index cd497b2..117c67e 100755
--- a/tools/releasetools/ota_from_target_files.py
+++ b/tools/releasetools/ota_from_target_files.py
@@ -778,11 +778,15 @@
 
   script.ShowProgress(system_progress, 0)
 
+  # See the notes in WriteBlockIncrementalOTAPackage().
+  allow_shared_blocks = target_info.get('ext4_share_dup_blocks') == "true"
+
   # Full OTA is done as an "incremental" against an empty source image. This
   # has the effect of writing new data from the package to the entire
   # partition, but lets us reuse the updater code that writes incrementals to
   # do it.
-  system_tgt = common.GetSparseImage("system", OPTIONS.input_tmp, input_zip)
+  system_tgt = common.GetSparseImage("system", OPTIONS.input_tmp, input_zip,
+                                     allow_shared_blocks)
   system_tgt.ResetFileMap()
   system_diff = common.BlockDifference("system", system_tgt, src=None)
   system_diff.WriteScript(script, output_zip)
@@ -793,7 +797,8 @@
   if HasVendorPartition(input_zip):
     script.ShowProgress(0.1, 0)
 
-    vendor_tgt = common.GetSparseImage("vendor", OPTIONS.input_tmp, input_zip)
+    vendor_tgt = common.GetSparseImage("vendor", OPTIONS.input_tmp, input_zip,
+                                       allow_shared_blocks)
     vendor_tgt.ResetFileMap()
     vendor_diff = common.BlockDifference("vendor", vendor_tgt)
     vendor_diff.WriteScript(script, output_zip)
@@ -970,8 +975,16 @@
   target_recovery = common.GetBootableImage(
       "/tmp/recovery.img", "recovery.img", OPTIONS.target_tmp, "RECOVERY")
 
-  system_src = common.GetSparseImage("system", OPTIONS.source_tmp, source_zip)
-  system_tgt = common.GetSparseImage("system", OPTIONS.target_tmp, target_zip)
+  # When target uses 'BOARD_EXT4_SHARE_DUP_BLOCKS := true', images may contain
+  # shared blocks (i.e. some blocks will show up in multiple files' block
+  # list). We can only allocate such shared blocks to the first "owner", and
+  # disable imgdiff for all later occurrences.
+  allow_shared_blocks = (source_info.get('ext4_share_dup_blocks') == "true" or
+                         target_info.get('ext4_share_dup_blocks') == "true")
+  system_src = common.GetSparseImage("system", OPTIONS.source_tmp, source_zip,
+                                     allow_shared_blocks)
+  system_tgt = common.GetSparseImage("system", OPTIONS.target_tmp, target_zip,
+                                     allow_shared_blocks)
 
   blockimgdiff_version = max(
       int(i) for i in target_info.get("blockimgdiff_versions", "1").split(","))
@@ -996,8 +1009,10 @@
   if HasVendorPartition(target_zip):
     if not HasVendorPartition(source_zip):
       raise RuntimeError("can't generate incremental that adds /vendor")
-    vendor_src = common.GetSparseImage("vendor", OPTIONS.source_tmp, source_zip)
-    vendor_tgt = common.GetSparseImage("vendor", OPTIONS.target_tmp, target_zip)
+    vendor_src = common.GetSparseImage("vendor", OPTIONS.source_tmp, source_zip,
+                                       allow_shared_blocks)
+    vendor_tgt = common.GetSparseImage("vendor", OPTIONS.target_tmp, target_zip,
+                                       allow_shared_blocks)
 
     # Check first block of vendor partition for remount R/W only if
     # disk type is ext4
diff --git a/tools/releasetools/sparse_img.py b/tools/releasetools/sparse_img.py
index c978be8..083da7a 100644
--- a/tools/releasetools/sparse_img.py
+++ b/tools/releasetools/sparse_img.py
@@ -33,7 +33,7 @@
   """
 
   def __init__(self, simg_fn, file_map_fn=None, clobbered_blocks=None,
-               mode="rb", build_map=True):
+               mode="rb", build_map=True, allow_shared_blocks=False):
     self.simg_f = f = open(simg_fn, mode)
 
     header_bin = f.read(28)
@@ -129,7 +129,8 @@
     self.extended = extended
 
     if file_map_fn:
-      self.LoadFileBlockMap(file_map_fn, self.clobbered_blocks)
+      self.LoadFileBlockMap(file_map_fn, self.clobbered_blocks,
+                            allow_shared_blocks)
     else:
       self.file_map = {"__DATA": self.care_map}
 
@@ -209,7 +210,14 @@
             yield fill_data * (this_read * (self.blocksize >> 2))
           to_read -= this_read
 
-  def LoadFileBlockMap(self, fn, clobbered_blocks):
+  def LoadFileBlockMap(self, fn, clobbered_blocks, allow_shared_blocks):
+    """Loads the given block map file.
+
+    Args:
+      fn: The filename of the block map file.
+      clobbered_blocks: A RangeSet instance for the clobbered blocks.
+      allow_shared_blocks: Whether having shared blocks is allowed.
+    """
     remaining = self.care_map
     self.file_map = out = {}
 
@@ -217,6 +225,18 @@
       for line in f:
         fn, ranges = line.split(None, 1)
         ranges = rangelib.RangeSet.parse(ranges)
+
+        if allow_shared_blocks:
+          # Find the shared blocks that have been claimed by others.
+          shared_blocks = ranges.subtract(remaining)
+          if shared_blocks:
+            ranges = ranges.subtract(shared_blocks)
+            if not ranges:
+              continue
+
+            # Tag the entry so that we can skip applying imgdiff on this file.
+            ranges.extra['uses_shared_blocks'] = True
+
         out[fn] = ranges
         assert ranges.size() == ranges.intersect(remaining).size()