diff --git a/assets/stan_demos/metaanalysis.stan b/assets/stan_demos/metaanalysis.stan
index 8b4957f..a403eea 100644
--- a/assets/stan_demos/metaanalysis.stan
+++ b/assets/stan_demos/metaanalysis.stan
@@ -1,5 +1,5 @@
 data {
-  int N;  // num experiments
+  int<lower=1> N;  // num experiments
   array[N] int<lower=0> successes;
   array[N] int<lower=0> failures;
 }