diff --git a/internal/restic/backend.go b/internal/restic/backend.go
index 07d0c1739..51198215f 100644
--- a/internal/restic/backend.go
+++ b/internal/restic/backend.go
@@ -34,6 +34,9 @@ type Backend interface {
 
 	// List runs fn for each file in the backend which has the type t. When an
 	// error occurs (or fn returns an error), List stops and returns it.
+	//
+	// The function fn is called in the same Goroutine that List() is called
+	// from.
 	List(ctx context.Context, t FileType, fn func(FileInfo) error) error
 
 	// IsNotExist returns true if the error was caused by a non-existing file
diff --git a/internal/restic/repository.go b/internal/restic/repository.go
index f1da9770c..1ab4a2766 100644
--- a/internal/restic/repository.go
+++ b/internal/restic/repository.go
@@ -26,7 +26,12 @@ type Repository interface {
 
 	LookupBlobSize(ID, BlobType) (uint, error)
 
-	List(context.Context, FileType, func(ID, int64) error) error
+	// List calls the function fn for each file of type t in the repository.
+	// When an error is returned by fn, processing stops and List() returns the
+	// error.
+	//
+	// The function fn is called in the same Goroutine List() was called from.
+	List(ctx context.Context, t FileType, fn func(ID, int64) error) error
 	ListPack(context.Context, ID) ([]Blob, int64, error)
 
 	Flush(context.Context) error