--- a/crates/nix-eval/src/session.rs
+++ b/crates/nix-eval/src/session.rs
@@ -225,6 +225,7 @@
 	) -> Result<Self> {
 		let mut cmd = Command::new("nix");
 		cmd.arg("repl")
+			.args(["--option", "pure-eval", "true"])
 			.arg(flake)
 			.arg("--log-format")
 			.arg("internal-json");