diff --git a/data/avro-schema/src/main/resources/avro/net/corda/data/membership/state/CommandMetadata.avsc b/data/avro-schema/src/main/resources/avro/net/corda/data/membership/state/CommandMetadata.avsc
new file mode 100644
index 0000000000..9fc8ef3b96
--- /dev/null
+++ b/data/avro-schema/src/main/resources/avro/net/corda/data/membership/state/CommandMetadata.avsc
@@ -0,0 +1,18 @@
+{
+  "type": "record",
+  "name": "CommandMetadata",
+  "namespace": "net.corda.data.membership.state",
+  "doc": "Metadata about a complete registration command.",
+  "fields": [
+    {
+      "name": "index",
+      "doc": "An index which can be used to determine the order of complete registration commands.",
+      "type": "int"
+    },
+    {
+      "name": "command",
+      "doc": "The name of the command which was completed.",
+      "type": "string"
+    }
+  ]
+}
\ No newline at end of file
diff --git a/data/avro-schema/src/main/resources/avro/net/corda/data/membership/state/RegistrationState.avsc b/data/avro-schema/src/main/resources/avro/net/corda/data/membership/state/RegistrationState.avsc
index 28a5d16297..e5979c988f 100644
--- a/data/avro-schema/src/main/resources/avro/net/corda/data/membership/state/RegistrationState.avsc
+++ b/data/avro-schema/src/main/resources/avro/net/corda/data/membership/state/RegistrationState.avsc
@@ -21,6 +21,15 @@
       "name": "mgm",
       "doc": "Holding identity of the MGM.",
       "type": "net.corda.data.identity.HoldingIdentity"
+    },
+    {
+      "name": "commands",
+      "doc": "A list of all the complete commands during registration. Can be used for idempotency in the case of message replays.",
+      "type": {
+        "type": "array",
+        "items": "net.corda.data.membership.state.CommandMetadata"
+      },
+      "default": []
     }
   ]
 }
\ No newline at end of file
diff --git a/data/avro-schema/src/test/kotlin/net/corda/data/command/registration/mgm/DeclineRegistrationCompatibilityTest.kt b/data/avro-schema/src/test/kotlin/net/corda/data/membership/command/registration/mgm/DeclineRegistrationCompatibilityTest.kt
similarity index 91%
rename from data/avro-schema/src/test/kotlin/net/corda/data/command/registration/mgm/DeclineRegistrationCompatibilityTest.kt
rename to data/avro-schema/src/test/kotlin/net/corda/data/membership/command/registration/mgm/DeclineRegistrationCompatibilityTest.kt
index fea285f523..130d61db8d 100644
--- a/data/avro-schema/src/test/kotlin/net/corda/data/command/registration/mgm/DeclineRegistrationCompatibilityTest.kt
+++ b/data/avro-schema/src/test/kotlin/net/corda/data/membership/command/registration/mgm/DeclineRegistrationCompatibilityTest.kt
@@ -1,6 +1,5 @@
-package net.corda.data.command.registration.mgm
+package net.corda.data.membership.command.registration.mgm
 
-import net.corda.data.membership.command.registration.mgm.DeclineRegistration
 import org.apache.avro.Schema
 import org.apache.avro.SchemaCompatibility
 import org.junit.jupiter.api.Assertions
diff --git a/data/avro-schema/src/test/kotlin/net/corda/data/membership/state/RegistrationStateTest.kt b/data/avro-schema/src/test/kotlin/net/corda/data/membership/state/RegistrationStateTest.kt
new file mode 100644
index 0000000000..3032520184
--- /dev/null
+++ b/data/avro-schema/src/test/kotlin/net/corda/data/membership/state/RegistrationStateTest.kt
@@ -0,0 +1,56 @@
+package net.corda.data.membership.state
+
+import net.corda.data.identity.HoldingIdentity
+import org.apache.avro.Schema
+import org.apache.avro.SchemaCompatibility
+import org.junit.jupiter.api.Assertions
+import org.junit.jupiter.api.Test
+
+class RegistrationStateTest {
+
+    @Test
+    fun `Changes in RegistrationState between Corda 5_0 and 5_1 are compatible`() {
+        val oldSchemaJson = """
+            {
+              "type": "record",
+              "name": "RegistrationState",
+              "namespace": "net.corda.data.membership.state",
+              "doc": "State for a registration.",
+              "fields": [
+                {
+                  "name": "registrationId",
+                  "doc": "UUID identifying this registration request",
+                  "type": {
+                    "type": "string",
+                    "logicalType": "uuid"
+                  }
+                },
+                {
+                  "name": "registeringMember",
+                  "doc": "Holding identity of the registering member as provided during P2P communication. Used to verify the registration request.",
+                  "type": "net.corda.data.identity.HoldingIdentity"
+                },
+                {
+                  "name": "mgm",
+                  "doc": "Holding identity of the MGM.",
+                  "type": "net.corda.data.identity.HoldingIdentity"
+                }
+              ]
+            }
+        """.trimIndent()
+
+        val oldSchema = Schema.Parser()
+            .addTypes(mapOf(HoldingIdentity::class.java.name to HoldingIdentity.`SCHEMA$`))
+            .parse(oldSchemaJson)
+        val newSchema = RegistrationState.`SCHEMA$`
+
+        val compatibility = SchemaCompatibility.checkReaderWriterCompatibility(newSchema, oldSchema)
+
+        Assertions.assertEquals(
+            compatibility.type,
+            SchemaCompatibility.SchemaCompatibilityType.COMPATIBLE,
+            "Failed due to incompatible change. ${compatibility.description}"
+        )
+    }
+
+}
\ No newline at end of file