diff --git a/shared/inc/values/Similarity.hpp b/shared/inc/values/Similarity.hpp
index f257082..29429bd 100644
--- a/shared/inc/values/Similarity.hpp
+++ b/shared/inc/values/Similarity.hpp
@@ -12,5 +12,5 @@ namespace Similarity
   // float needleman_wunsch(Dna *d1, Dna *d2); used for bioinformatics and aligment. Dont need its aligned alredy
 
   typedef float(simil_func)(Dna *d1, Dna *d2);
-  float calc_similarity(std::vector<Dna> vec, simil_func f);
+  float calc_similarity(std::vector<Dna> &vec, simil_func f);
 }
\ No newline at end of file
diff --git a/shared/src/values/Similarity.cpp b/shared/src/values/Similarity.cpp
index 197f6ea..ee5be8d 100644
--- a/shared/src/values/Similarity.cpp
+++ b/shared/src/values/Similarity.cpp
@@ -96,7 +96,7 @@ namespace Similarity
     return 1 - (ld / sizeof(Dna));
   }
 
-  float calc_similarity(std::vector<Dna> vec, simil_func f)
+  float calc_similarity(std::vector<Dna> &vec, simil_func f)
   {
     size_t num_pairs = (vec.size() * (vec.size() - 1)) / 2;