diff --git a/src/Serialization/Rings.jl b/src/Serialization/Rings.jl
index 9da031fc6fa4..c1e854b8c339 100644
--- a/src/Serialization/Rings.jl
+++ b/src/Serialization/Rings.jl
@@ -47,6 +47,7 @@ type_params(x::T) where T <: IdealUnionType = TypeParams(T, base_ring(x))
 # exclude from ring union
 type_params(::ZZRing) = TypeParams(ZZRing, nothing)
 type_params(::ZZRingElem) = TypeParams(ZZRingElem, nothing)
+type_params(R::T) where T <: PolyRingUnionType = TypeParams(T, coefficient_ring(R))
 type_params(R::T) where T <: ModRingUnion = TypeParams(T, nothing)
 
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