diff --git a/functions/quantile_function/student_t_qf.stanfunctions b/functions/quantile_function/student_t_qf.stanfunctions
index 0ef179c..08e3e43 100644
--- a/functions/quantile_function/student_t_qf.stanfunctions
+++ b/functions/quantile_function/student_t_qf.stanfunctions
@@ -293,7 +293,7 @@ real student_t_log_qf(real log_p, real ndf) {
     y = exp(2 * x);
     
     if ((ndf < 2.1 && P > 0.5) || y > 0.05 + a) {
-      x = inv_Phi(log_P2);
+      x = inv_Phi(0.5 * P);
       y = square(x);
       
       if (ndf < 5) {
@@ -333,4 +333,4 @@ vector student_t_log_qf(vector u, real nu) {
   
   return x;
 }
-/** @} */
\ No newline at end of file
+/** @} */