diff --git a/benchmark/herk.c b/benchmark/herk.c
index d2e25ff46..bd336e6b1 100644
--- a/benchmark/herk.c
+++ b/benchmark/herk.c
@@ -162,8 +162,8 @@ int main(int argc, char *argv[]){
 
     for(j = 0; j < m; j++){
       for(i = 0; i < m * COMPSIZE; i++){
-	a[i + j * m * COMPSIZE] = ((FLOAT) rand() / (FLOAT) RAND_MAX) - 0.5;
-	c[i + j * m * COMPSIZE] = ((FLOAT) rand() / (FLOAT) RAND_MAX) - 0.5;
+	a[(long)i + (long)j * (long)m * COMPSIZE] = ((FLOAT) rand() / (FLOAT) RAND_MAX) - 0.5;
+	c[(long)i + (long)j * (long)m * COMPSIZE] = ((FLOAT) rand() / (FLOAT) RAND_MAX) - 0.5;
       }
     }