diff --git a/pila.c b/pila.c
index 26b3881..0ad140c 100644
--- a/pila.c
+++ b/pila.c
@@ -374,6 +374,10 @@ compile_anon_start_nat(RpnState *st)
 void
 compile_end_nat(RpnState *st)
 {
+	if (!st->compiling) {
+		signal_error(st, "not in compiling mode");
+		return;
+	}
 	Word *w = malloc(sizeof(*w));
 
 	st->compiling = false;