diff --git a/src/statictype.jl b/src/statictype.jl
index 9f5d759..ec70725 100644
--- a/src/statictype.jl
+++ b/src/statictype.jl
@@ -9,7 +9,7 @@ return `Nullable(n)`. Otherwise, return `Nullable{Int}()`.
 length(::Type{Union{}}) = Nullable(0)
 length(::Type) = Nullable{Int}()
 length{T<:Pair}(::Type{T}) = 2
-if VERSION < v"0.6-"
+if VERSION < v"0.6.0-dev.2123" # where syntax introduced by julia PR #18457
     length{T<:Tuple}(::Type{T}) = Nullable{Int}(Base.length(T.parameters))
 else
     include_string("""