diff --git a/src/fava/serialisation.py b/src/fava/serialisation.py
index bbec34952..461dc4743 100644
--- a/src/fava/serialisation.py
+++ b/src/fava/serialisation.py
@@ -21,6 +21,7 @@
 from fava.beans import create
 from fava.beans.abc import Amount
 from fava.beans.abc import Balance
+from fava.beans.abc import Custom
 from fava.beans.abc import Directive
 from fava.beans.abc import Posting
 from fava.beans.abc import Transaction
@@ -60,6 +61,15 @@ def _(entry: Transaction) -> Any:
     return ret
 
 
+@serialise.register(Custom)
+def _(entry: Custom) -> Any:
+    """Serialise an entry."""
+    ret = entry._asdict()  # type: ignore[attr-defined]
+    ret["t"] = "Custom"
+    ret["values"] = [v.value for v in entry.values]
+    return ret
+
+
 @serialise.register(Balance)
 def _(entry: Balance) -> Any:
     """Serialise an entry."""
diff --git a/tests/__snapshots__/test_serialisation-test_serialise_entry_types.json b/tests/__snapshots__/test_serialisation-test_serialise_entry_types.json
index 31a9cf711..8c817fb25 100644
--- a/tests/__snapshots__/test_serialisation-test_serialise_entry_types.json
+++ b/tests/__snapshots__/test_serialisation-test_serialise_entry_types.json
@@ -1,4 +1,20 @@
 [
+  {
+    "date": "2012-12-12",
+    "meta": {
+      "filename": "<string>",
+      "lineno": 20
+    },
+    "t": "Custom",
+    "type": "string",
+    "values": [
+      {
+        "currency": "EUR",
+        "number": 1
+      },
+      false
+    ]
+  },
   {
     "account": "Assets:Cash",
     "booking": "Booking.STRICT",
@@ -138,7 +154,7 @@
     "date": "2019-12-12",
     "meta": {
       "filename": "<string>",
-      "lineno": 21
+      "lineno": 22
     },
     "name": "query name",
     "query_string": "journal",
diff --git a/tests/test_serialisation.py b/tests/test_serialisation.py
index 89d1e2adf..66399e3ce 100644
--- a/tests/test_serialisation.py
+++ b/tests/test_serialisation.py
@@ -98,6 +98,7 @@ def test_serialise_entry_types(
 
     2018-12-15 commodity USD
     2018-12-16 price USD 1 EUR
+    2012-12-12 custom "string" 1 EUR FALSE
 
     2019-12-12 query "query name" "journal"
     """