diff --git a/src/lib/ffi.pl b/src/lib/ffi.pl
index 35a56195..385d8c79 100644
--- a/src/lib/ffi.pl
+++ b/src/lib/ffi.pl
@@ -146,7 +146,6 @@ allocate(Allocator, Type, Args, Ptr) :-
 % For type cstr take read a nul-terminated utf-8 string starting at Ptr.
 %
 read_ptr(Type, Ptr, Value) :-
-    must_be(var, Value),
     must_be(atom, Type),
     must_be(integer, Ptr),
     '$ffi_read_ptr'(Type, Ptr, Value).