diff --git a/base/some.jl b/base/some.jl
index 73e65ac6399b5..b63f1ab3016ed 100644
--- a/base/some.jl
+++ b/base/some.jl
@@ -45,6 +45,9 @@ notnothing(::Nothing) = throw(ArgumentError("nothing passed to notnothing"))
     isnothing(x)
 
 Return `true` if `x === nothing`, and return `false` if not.
+
+!!! compat "Julia 1.1"
+    This function requires at least Julia 1.1.
 """
 isnothing(::Any) = false
 isnothing(::Nothing) = true