diff --git a/base/reflection.jl b/base/reflection.jl
index 3464dc9c398a3..70b149f85833f 100644
--- a/base/reflection.jl
+++ b/base/reflection.jl
@@ -408,6 +408,9 @@ false
 julia> ismutable([1,2])
 true
 ```
+
+!!! compat "Julia 1.5"
+    This function requires at least Julia 1.5.
 """
 ismutable(@nospecialize(x)) = (@_pure_meta; typeof(x).mutable)