diff --git a/test/iterators.jl b/test/iterators.jl
index 9dd1fdd2e34901..0fba22e139370a 100644
--- a/test/iterators.jl
+++ b/test/iterators.jl
@@ -1023,10 +1023,12 @@ end
     simple_types = (Vector, NTuple, NamedTuple{X, Y} where {X, Y <: NTuple})
     @testset "f: $f" for f ∈ functions
         for V ∈ simple_types
+            @test Core.Compiler.is_foldable(Base.infer_effects(f, Tuple{V}))
             @test Core.Compiler.is_foldable(Base.infer_effects(f, Tuple{Type{<:V}}))
             for U ∈ iterator_types
                 S = U{<:V}
                 ((U <: Iterators.Zip) || (U <: Iterators.Flatten)) && continue  # partially broken
+                @test Core.Compiler.is_foldable(Base.infer_effects(f, Tuple{S}))
                 @test Core.Compiler.is_foldable(Base.infer_effects(f, Tuple{Type{<:S}}))
             end
         end