diff --git a/src/gpu/mblas/nth_element.cu b/src/gpu/mblas/nth_element.cu
index 8cce38c0..8e13e828 100644
--- a/src/gpu/mblas/nth_element.cu
+++ b/src/gpu/mblas/nth_element.cu
@@ -254,7 +254,7 @@ __global__ void gGetValueByKey(float* d_in, float* d_out, int* indeces, int n)
 
 NthElement::NthElement(size_t maxBeamSize, size_t maxBatchSize, cudaStream_t& stream)
     : stream_(stream),
-      NUM_BLOCKS(std::max(500, int(maxBeamSize * 85000 / (2 * BLOCK_SIZE)) + int(maxBeamSize * 85000 % (2 * BLOCK_SIZE) != 0)))
+      NUM_BLOCKS(std::min(500, int(maxBeamSize * 85000 / (2 * BLOCK_SIZE)) + int(maxBeamSize * 85000 % (2 * BLOCK_SIZE) != 0)))
 {
   HANDLE_ERROR( cudaMalloc((void**)&d_ind, maxBatchSize * NUM_BLOCKS * sizeof(int)) );