diff --git a/test/runtests.jl b/test/runtests.jl
index 7a2ccf5..b0935d0 100644
--- a/test/runtests.jl
+++ b/test/runtests.jl
@@ -190,7 +190,7 @@ end
     @test eltype(mappedarray(identity, [missing, 1])) == Union{Missing, Int}
 
     # ReadonlyMappedArray and MappedArray
-    _zero(x) = x > 0 ? x : 0
+    _zero(x) = ismissing(x) ? x : (x > 0 ? x : 0)
     @test eltype(mappedarray(_zero, [1, 1.0])) == Union{Float64,Int}
     @test eltype(mappedarray(_zero, [1.0, 1])) == Union{Float64,Int}
     @test eltype(mappedarray(_zero, [1, 1])) == Int