diff --git a/.changeset/dirty-wolves-wash.md b/.changeset/dirty-wolves-wash.md
new file mode 100644
index 0000000000..4ffbb89725
--- /dev/null
+++ b/.changeset/dirty-wolves-wash.md
@@ -0,0 +1,5 @@
+---
+"@core/sync-service": patch
+---
+
+Fix root table parameter validation to return 400 when missing
diff --git a/packages/sync-service/lib/electric/plug/serve_shape_plug.ex b/packages/sync-service/lib/electric/plug/serve_shape_plug.ex
index 7fca9241f7..bad8e694b8 100644
--- a/packages/sync-service/lib/electric/plug/serve_shape_plug.ex
+++ b/packages/sync-service/lib/electric/plug/serve_shape_plug.ex
@@ -153,6 +153,8 @@ defmodule Electric.Plug.ServeShapePlug do
       end
     end
 
+    def cast_root_table(%Ecto.Changeset{valid?: false} = changeset, _), do: changeset
+
     def cast_root_table(%Ecto.Changeset{} = changeset, opts) do
       table = fetch_change!(changeset, :table)
       where = fetch_field!(changeset, :where)
diff --git a/packages/sync-service/test/electric/plug/serve_shape_plug_test.exs b/packages/sync-service/test/electric/plug/serve_shape_plug_test.exs
index 0b98c8c1bb..cf395216a5 100644
--- a/packages/sync-service/test/electric/plug/serve_shape_plug_test.exs
+++ b/packages/sync-service/test/electric/plug/serve_shape_plug_test.exs
@@ -152,22 +152,43 @@ defmodule Electric.Plug.ServeShapePlugTest do
       :with_tenant_id
     ]
 
-    test "returns 400 for invalid params", ctx do
+    test "returns 400 for invalid table", ctx do
       conn =
         ctx
-        |> conn(:get, %{"table" => ".invalid_shape"}, "?offset=invalid")
+        |> conn(:get, %{"table" => ".invalid_shape"}, "?offset=-1")
         |> ServeShapePlug.call([])
 
       assert conn.status == 400
 
       assert Jason.decode!(conn.resp_body) == %{
-               "offset" => ["has invalid format"],
                "table" => [
                  "Invalid zero-length delimited identifier"
                ]
              }
     end
 
+    test "returns 400 for invalid offset", ctx do
+      conn =
+        ctx
+        |> conn(:get, %{"table" => "foo"}, "?offset=invalid")
+        |> ServeShapePlug.call([])
+
+      assert conn.status == 400
+
+      assert Jason.decode!(conn.resp_body) == %{"offset" => ["has invalid format"]}
+    end
+
+    test "returns 400 when table param is missing", ctx do
+      conn =
+        ctx
+        |> conn(:get, %{}, "?offset=-1")
+        |> ServeShapePlug.call([])
+
+      assert conn.status == 400
+
+      assert %{"table" => ["can't be blank"]} = Jason.decode!(conn.resp_body)
+    end
+
     test "returns 400 when table does not exist", ctx do
       # this will pass table name validation
       # but will fail to find the table