diff --git a/pkg/icingadb/v1/customvar.go b/pkg/icingadb/v1/customvar.go
index 56f2b81e..fd8d3c09 100644
--- a/pkg/icingadb/v1/customvar.go
+++ b/pkg/icingadb/v1/customvar.go
@@ -1,8 +1,16 @@
 package v1
 
 import (
+	"context"
+	"encoding/json"
+	"fmt"
+	"github.com/icinga/icingadb/pkg/com"
 	"github.com/icinga/icingadb/pkg/contracts"
+	"github.com/icinga/icingadb/pkg/flatten"
 	"github.com/icinga/icingadb/pkg/types"
+	"github.com/icinga/icingadb/pkg/utils"
+	"golang.org/x/sync/errgroup"
+	"runtime"
 )
 
 type Customvar struct {
@@ -26,3 +34,61 @@ func NewCustomvar() contracts.Entity {
 func NewCustomvarFlat() contracts.Entity {
 	return &CustomvarFlat{}
 }
+
+// FlattenCustomvars creates and yields flat custom variables from the provided custom variables.
+func FlattenCustomvars(ctx context.Context, cvs <-chan contracts.Entity) (<-chan contracts.Entity, <-chan error) {
+	cvFlats := make(chan contracts.Entity)
+	g, ctx := errgroup.WithContext(ctx)
+
+	g.Go(func() error {
+		defer close(cvFlats)
+
+		g, _ := errgroup.WithContext(ctx)
+
+		for i := 0; i < runtime.NumCPU(); i++ {
+			g.Go(func() error {
+				for entity := range cvs {
+					var value interface{}
+					customvar := entity.(*Customvar)
+					if err := json.Unmarshal([]byte(customvar.Value), &value); err != nil {
+						return err
+					}
+
+					flattened := flatten.Flatten(value, customvar.Name)
+
+					for flatname, flatvalue := range flattened {
+						flatvalue := fmt.Sprintf("%v", flatvalue)
+						select {
+						case cvFlats <- &CustomvarFlat{
+							CustomvarMeta: CustomvarMeta{
+								EntityWithoutChecksum: EntityWithoutChecksum{
+									IdMeta: IdMeta{
+										// TODO(el): Schema comment is wrong.
+										// Without customvar.Id we would produce duplicate keys here.
+										Id: utils.Checksum(customvar.EnvironmentId.String() + customvar.Id.String() + flatname + flatvalue),
+									},
+								},
+								EnvironmentMeta: EnvironmentMeta{
+									EnvironmentId: customvar.EnvironmentId,
+								},
+								CustomvarId: customvar.Id,
+							},
+							Flatname:         flatname,
+							FlatnameChecksum: utils.Checksum(flatname),
+							Flatvalue:        flatvalue,
+						}:
+						case <-ctx.Done():
+							return ctx.Err()
+						}
+					}
+				}
+
+				return nil
+			})
+		}
+
+		return g.Wait()
+	})
+
+	return cvFlats, com.WaitAsync(g)
+}