diff --git a/paddle/fluid/operators/multinomial_op.h b/paddle/fluid/operators/multinomial_op.h
index cb63fc01972539460a21e8be990dec0996c31944..c025fc3d6ff3c9963d8103d8d852cf4ee46491be 100644
--- a/paddle/fluid/operators/multinomial_op.h
+++ b/paddle/fluid/operators/multinomial_op.h
@@ -31,7 +31,7 @@ void MultinomialFunctor(T* out_data, const T* in_data,
                         const int64_t num_samples, const bool replacement,
                         const int64_t num_categories,
                         const int64_t num_distributions) {
-  int64_t C = num_categories;
+  int64_t C = num_categories + 1;
   T cumulative_probs[C];
 
   std::uniform_real_distribution<T> dist(0, 1);