diff --git a/modules/flann/include/opencv2/flann/kdtree_index.h b/modules/flann/include/opencv2/flann/kdtree_index.h
index 8245f7db79..ed17cecb7c 100644
--- a/modules/flann/include/opencv2/flann/kdtree_index.h
+++ b/modules/flann/include/opencv2/flann/kdtree_index.h
@@ -46,6 +46,11 @@
 #include "random.h"
 #include "saving.h"
 
+#if defined(__clang__) || defined(__GNUC__)
+#define CV_RESTRICT __restrict__
+#else
+#define CV_RESTRICT
+#endif
 
 namespace cvflann
 {
@@ -320,9 +325,7 @@ private:
         int cnt = std::min((int)SAMPLE_MEAN+1, count);
         for (int j = 0; j < cnt; ++j) {
             ElementType* v = dataset_[ind[j]];
-            for (size_t k=0; k<veclen_; ++k) {
-                mean_[k] += v[k];
-            }
+            Sum(v, veclen_, mean_);
         }
         for (size_t k=0; k<veclen_; ++k) {
             mean_[k] /= cnt;
@@ -331,10 +334,7 @@ private:
         /* Compute variances (no need to divide by count). */
         for (int j = 0; j < cnt; ++j) {
             ElementType* v = dataset_[ind[j]];
-            for (size_t k=0; k<veclen_; ++k) {
-                DistanceType dist = v[k] - mean_[k];
-                var_[k] += dist * dist;
-            }
+            Var(v, mean_, veclen_, var_);
         }
         /* Select one of the highest variance indices at random. */
         cutfeat = selectDivision(var_);
@@ -584,6 +584,18 @@ private:
         RAND_DIM=5
     };
 
+    void Sum(const ElementType* CV_RESTRICT data, size_t len, DistanceType* CV_RESTRICT mean) {
+        for (size_t k=0; k<len; ++k) {
+            mean[k] += data[k];
+        }
+    }
+
+    void Var(const ElementType* CV_RESTRICT data, const DistanceType* CV_RESTRICT mean, size_t len, DistanceType*CV_RESTRICT var) {
+        for (size_t k=0; k<len; ++k) {
+            DistanceType dist = data[k] - mean[k];
+            var[k] += dist * dist;
+        }
+    }
 
     /**
      * Number of randomized trees that are used