diff --git a/src/strings.jl b/src/strings.jl
index bed60f3..d6af63b 100644
--- a/src/strings.jl
+++ b/src/strings.jl
@@ -3,9 +3,11 @@ struct PointerString <: AbstractString
     len::Int
 end
 
-function Base.hash(s::PointerString, h::UInt)
-    h += Base.memhash_seed
-    ccall(Base.memhash, UInt, (Ptr{UInt8}, Csize_t, UInt32), s.ptr, s.len, h % UInt32) + h
+if isdefined(Base, :memhash)
+    function Base.hash(s::PointerString, h::UInt)
+        h += Base.memhash_seed
+        ccall(Base.memhash, UInt, (Ptr{UInt8}, Csize_t, UInt32), s.ptr, s.len, h % UInt32) + h
+    end
 end
 
 import Base: ==