diff --git a/rebar.config b/rebar.config
index be9005679..acd737681 100644
--- a/rebar.config
+++ b/rebar.config
@@ -88,8 +88,8 @@
             {if_var_match, db_type, mssql, {d, 'mssql'}},
             {if_var_true, elixir, {d, 'ELIXIR_ENABLED'}},
             {if_var_true, erlang_deprecated_types, {d, 'ERL_DEPRECATED_TYPES'}},
-	    {if_version_above, "18", {d, 'STRONG_RAND_BYTES'}},
-	    {if_version_above, "17", {d, 'GB_SETS_ITERATOR_FROM'}},
+	    {if_have_fun, {crypto, strong_rand_bytes, 1}, {d, 'STRONG_RAND_BYTES'}},
+	    {if_have_fun, {gb_sets, iterator_from, 2}, {d, 'GB_SETS_ITERATOR_FROM'}},
 	    {if_have_fun, {public_key, short_name_hash, 1}, {d, 'SHORT_NAME_HASH'}},
             {if_var_true, hipe, native},
             {src_dirs, [asn1, src,