diff --git a/R/primary_censored_dist.R b/R/primary_censored_dist.R
index 60ef7eb..299499b 100644
--- a/R/primary_censored_dist.R
+++ b/R/primary_censored_dist.R
@@ -285,6 +285,9 @@ primary_censored_cdf.pcens_pweibull_dunif <- function(
     # Use the lower incomplete gamma function
     scaled_t <- (t * inv_scale)^shape
     vapply(scaled_t, function(x) {
+      if (x <= 0) {
+        return(0)
+      }
       pracma::gammainc(x, 1 + inv_shape)["lowinc"]
     }, numeric(1))
   }
diff --git a/inst/stan/functions/primary_censored_dist_analytical_cdf.stan b/inst/stan/functions/primary_censored_dist_analytical_cdf.stan
index 6030fa2..ff4d715 100644
--- a/inst/stan/functions/primary_censored_dist_analytical_cdf.stan
+++ b/inst/stan/functions/primary_censored_dist_analytical_cdf.stan
@@ -126,7 +126,7 @@ real primary_censored_lognormal_uniform_lcdf(data real d, real q, array[] real p
 }
 
 /**
-  * Compute the log of the integral of the Weibull PDF from 0 to t
+  * Compute the log of the lower incomplete gamma function
   *
   * This function is used in the analytical solution for the primary censored
   * Weibull distribution with uniform primary censoring. It corresponds to the