diff --git a/refinery/units/meta/dedup.py b/refinery/units/meta/dedup.py
index 88b21e192..29eaebf62 100644
--- a/refinery/units/meta/dedup.py
+++ b/refinery/units/meta/dedup.py
@@ -1,35 +1,62 @@
 #!/usr/bin/env python3
 # -*- coding: utf-8 -*-
 from refinery.units import Unit, Arg
+from refinery.lib.tools import isbuffer
+from refinery.lib.meta import metavars
+from refinery.lib.argformats import PythonExpression
+
+from hashlib import md5
 
 
 class dedup(Unit):
     """
     Deduplicates a sequence of multiple inputs. The deduplication is limited to the current `refinery.lib.frame`.
     """
-    def __init__(self, count: Arg.Switch('-c', help='Store the count of each deduplicated chunk.') = False):
-        super().__init__(count=count)
+    def __init__(
+        self,
+        key: Arg('key', type=str, help='An optional meta variable expression to deduplicate.') = None,
+        count: Arg.Switch('-c', help='Store the count of each deduplicated chunk.') = False
+    ):
+        super().__init__(key=key, count=count)
 
     def filter(self, chunks):
+        keyvar = self.args.key
+
+        if keyvar is not None:
+            def key(chunk):
+                v = PythonExpression.Evaluate(keyvar, metavars(chunk))
+                if isbuffer(v):
+                    v = md5(v).digest()
+                return v
+        else:
+            def key(chunk):
+                return md5(chunk).digest()
+
         if self.args.count:
-            from collections import Counter
-            barrier = Counter(chunks)
-            for chunk in chunks:
-                if not chunk.visible:
-                    yield chunk
-                    continue
-                barrier.update(chunk)
-            for chunk, count in barrier.items():
-                chunk.meta['count'] = count
-                yield chunk
+            counts = {}
+            buffer = {}
+            hashes = None
         else:
-            from hashlib import md5
-            barrier = set()
-            for chunk in chunks:
-                if not chunk.visible:
-                    yield chunk
-                    continue
-                hashed = md5(chunk).digest()
-                if hashed not in barrier:
-                    barrier.add(hashed)
-                    yield chunk
+            hashes = set()
+            counts = None
+            buffer = None
+
+        for chunk in chunks:
+            if not chunk.visible:
+                yield chunk
+                continue
+
+            uid = key(chunk)
+
+            if hashes is None:
+                counts[uid] = counts.get(uid, 0) + 1
+                buffer.setdefault(uid, chunk)
+            elif uid in hashes:
+                continue
+            else:
+                hashes.add(uid)
+                yield chunk
+
+        if hashes is None:
+            for uid, chunk in buffer.items():
+                yield self.labelled(chunk, count=counts[uid])
diff --git a/test/units/meta/test_dedup.py b/test/units/meta/test_dedup.py
index bd8c3932b..91b7190ec 100644
--- a/test/units/meta/test_dedup.py
+++ b/test/units/meta/test_dedup.py
@@ -39,3 +39,7 @@ def test_duplicated_strings(self):
     def test_count(self):
         pipeline = L('emit HELLO-WORLD [| push [| rex . | dedup -c | sorted count | pick :2 | pop t s ]| cfmt {t}{s} ]')
         self.assertEqual(pipeline(), B'LO')
+
+    def test_key(self):
+        pipeline = L('emit FOO BAR BAZ BAMPF [| dedup size ]')
+        self.assertEqual(pipeline(), B'FOOBAMPF')