diff --git a/ratatool-diffy/src/main/scala/com/spotify/ratatool/diffy/BigDiffy.scala b/ratatool-diffy/src/main/scala/com/spotify/ratatool/diffy/BigDiffy.scala
index 52ca5294..9cca7ef1 100644
--- a/ratatool-diffy/src/main/scala/com/spotify/ratatool/diffy/BigDiffy.scala
+++ b/ratatool-diffy/src/main/scala/com/spotify/ratatool/diffy/BigDiffy.scala
@@ -29,7 +29,7 @@ import com.spotify.scio.values.SCollection
 import com.twitter.algebird._
 import org.apache.avro.Schema
 import org.apache.avro.generic.GenericRecord
-import org.apache.beam.sdk.io.{FileSystems, TextIO}
+import org.apache.beam.sdk.io.TextIO
 
 import scala.annotation.tailrec
 import scala.collection.JavaConverters._
@@ -383,7 +383,7 @@ object BigDiffy extends Command {
         |
         |  --input-mode=(avro|bigquery)     Diff-ing Avro or BQ records
         |  [--output-mode=(gcs|bigquery)]   Saves to a text file in GCS or a BigQuery dataset. Defaults to GCS
-        |  --key=<key>                      '.' separated key field
+        |  --key=<key>                      '.' separated key field. Specify multiple --key params for multi key usage.
         |  --lhs=<path>                     LHS File path or BigQuery table
         |  --rhs=<path>                     RHS File path or BigQuery table
         |  --output=<output>                File path prefix for output
@@ -411,7 +411,7 @@ object BigDiffy extends Command {
     sys.exit(1)
   }
 
-  private def avroKeyFn(keys: Seq[String]): GenericRecord => String = {
+  private[diffy] def avroKeyFn(keys: Seq[String]): GenericRecord => String = {
     @tailrec
     def get(xs: Array[String], i: Int, r: GenericRecord): String =
       if (i == xs.length - 1) {
@@ -424,7 +424,7 @@ object BigDiffy extends Command {
     (r: GenericRecord) =>  xs.map { x => get(x, 0, r) }.mkString("_")
   }
 
-  private def tableRowKeyFn(keys: Seq[String]): TableRow => String = {
+  private[diffy] def tableRowKeyFn(keys: Seq[String]): TableRow => String = {
     @tailrec
     def get(xs: Array[String], i: Int, r: java.util.Map[String, AnyRef]): String =
       if (i == xs.length - 1) {
diff --git a/ratatool-diffy/src/test/scala/com/spotify/ratatool/diffy/BigDiffyTest.scala b/ratatool-diffy/src/test/scala/com/spotify/ratatool/diffy/BigDiffyTest.scala
index b37bb7a3..cd1f399c 100644
--- a/ratatool-diffy/src/test/scala/com/spotify/ratatool/diffy/BigDiffyTest.scala
+++ b/ratatool-diffy/src/test/scala/com/spotify/ratatool/diffy/BigDiffyTest.scala
@@ -17,15 +17,18 @@
 
 package com.spotify.ratatool.diffy
 
-import com.spotify.ratatool.avro.specific.{RequiredNestedRecord, TestRecord}
-import com.spotify.ratatool.scalacheck._
-import com.spotify.scio.testing.PipelineSpec
 import org.apache.avro.util.Utf8
 import org.apache.beam.sdk.coders.AvroCoder
 import org.apache.beam.sdk.util.CoderUtils
 import org.scalacheck.Gen
 import org.scalacheck.rng.Seed
 
+import com.spotify.ratatool.avro.specific.{RequiredNestedRecord, TestRecord}
+import com.spotify.ratatool.scalacheck._
+import com.spotify.scio.testing.PipelineSpec
+
+import com.google.api.services.bigquery.model.TableRow
+
 class BigDiffyTest extends PipelineSpec {
 
   val keys = (1 to 1000).map("key" + _)
@@ -116,4 +119,41 @@ class BigDiffyTest extends PipelineSpec {
     }
   }
 
+  "BigDiffy avroKeyFn" should "work with single key" in {
+    val record = specificRecordOf[TestRecord].sample.get
+    val keyValue = BigDiffy.avroKeyFn(Seq("required_fields.int_field"))(record)
+
+    keyValue shouldBe record.getRequiredFields.getIntField.toString
+  }
+
+  "BigDiffy avroKeyFn" should "work with multiple key" in {
+    val record = specificRecordOf[TestRecord].sample.get
+    val keys = Seq("required_fields.int_field", "required_fields.double_field")
+    val keyValues = BigDiffy.avroKeyFn(keys)(record)
+    val expectedKey =
+      s"${record.getRequiredFields.getIntField}_${record.getRequiredFields.getDoubleField}"
+
+    keyValues shouldBe expectedKey
+  }
+
+  "BigDiffy tableRowKeyFn" should "work with single key" in {
+    val record = new TableRow()
+    record.set("key", "foo")
+    val keyValue = BigDiffy.tableRowKeyFn(Seq("key"))(record)
+
+    keyValue shouldBe "foo"
+  }
+
+  "BigDiffy tableRowKeyFn" should "work with multiple key" in {
+    val subRecord = new TableRow()
+    subRecord.set("key", "foo")
+    subRecord.set("other_key", "bar")
+    val record = new TableRow()
+    record.set("record", subRecord)
+
+    val keys = Seq("record.key", "record.other_key")
+    val keyValues = BigDiffy.tableRowKeyFn(keys)(record.asInstanceOf[TableRow])
+
+    keyValues shouldBe "foo_bar"
+  }
 }