diff --git a/modules/video/src/ecc.cpp b/modules/video/src/ecc.cpp
index f56e1f24b..8c5fbee79 100644
--- a/modules/video/src/ecc.cpp
+++ b/modules/video/src/ecc.cpp
@@ -297,7 +297,12 @@ static void update_warping_matrix_ECC (Mat& map_matrix, const Mat& update, const
         mapPtr[5] += updatePtr[7];
     }
     if (motionType == MOTION_EUCLIDEAN) {
-        double new_theta = acos(mapPtr[0]) + updatePtr[0];
+        double new_theta = updatePtr[0];
+        if (mapPtr[3]>0)
+            new_theta += acos(mapPtr[0]);
+
+        if (mapPtr[3]<0)
+            new_theta -= acos(mapPtr[0]);
 
         mapPtr[2] += updatePtr[1];
         mapPtr[5] += updatePtr[2];
diff --git a/modules/video/src/optflowgf.cpp b/modules/video/src/optflowgf.cpp
index 4225e3d7f..27abf739f 100644
--- a/modules/video/src/optflowgf.cpp
+++ b/modules/video/src/optflowgf.cpp
@@ -43,6 +43,10 @@
 #include "precomp.hpp"
 #include "opencl_kernels_video.hpp"
 
+#if defined __APPLE__ || defined ANDROID
+#define SMALL_LOCALSIZE
+#endif
+
 //
 // 2D dense optical flow algorithm from the following paper:
 // Gunnar Farneback. "Two-Frame Motion Estimation Based on Polynomial Expansion".
@@ -836,7 +840,7 @@ private:
 
     bool gaussianBlurOcl(const UMat &src, int ksizeHalf, UMat &dst)
     {
-#ifdef ANDROID
+#ifdef SMALL_LOCALSIZE
         size_t localsize[2] = { 128, 1};
 #else
         size_t localsize[2] = { 256, 1};
@@ -863,7 +867,7 @@ private:
     bool gaussianBlur5Ocl(const UMat &src, int ksizeHalf, UMat &dst)
     {
         int height = src.rows / 5;
-#ifdef ANDROID
+#ifdef SMALL_LOCALSIZE
         size_t localsize[2] = { 128, 1};
 #else
         size_t localsize[2] = { 256, 1};
@@ -888,7 +892,7 @@ private:
     }
     bool polynomialExpansionOcl(const UMat &src, UMat &dst)
     {
-#ifdef ANDROID
+#ifdef SMALL_LOCALSIZE
         size_t localsize[2] = { 128, 1};
 #else
         size_t localsize[2] = { 256, 1};
@@ -925,7 +929,7 @@ private:
     bool boxFilter5Ocl(const UMat &src, int ksizeHalf, UMat &dst)
     {
         int height = src.rows / 5;
-#ifdef ANDROID
+#ifdef SMALL_LOCALSIZE
         size_t localsize[2] = { 128, 1};
 #else
         size_t localsize[2] = { 256, 1};
@@ -952,7 +956,7 @@ private:
 
     bool updateFlowOcl(const UMat &M, UMat &flowx, UMat &flowy)
     {
-#ifdef ANDROID
+#ifdef SMALL_LOCALSIZE
         size_t localsize[2] = { 32, 4};
 #else
         size_t localsize[2] = { 32, 8};
@@ -976,7 +980,7 @@ private:
     }
     bool updateMatricesOcl(const UMat &flowx, const UMat &flowy, const UMat &R0, const UMat &R1, UMat &M)
     {
-#ifdef ANDROID
+#ifdef SMALL_LOCALSIZE
         size_t localsize[2] = { 32, 4};
 #else
         size_t localsize[2] = { 32, 8};
diff --git a/samples/cpp/fback.cpp b/samples/cpp/fback.cpp
index 476cfe654..af0f2ca09 100644
--- a/samples/cpp/fback.cpp
+++ b/samples/cpp/fback.cpp
@@ -37,7 +37,8 @@ int main(int, char**)
     if( !cap.isOpened() )
         return -1;
 
-    Mat prevgray, gray, flow, cflow, frame;
+    Mat flow, cflow, frame;
+    UMat gray, prevgray, uflow;
     namedWindow("flow", 1);
 
     for(;;)
@@ -45,10 +46,11 @@ int main(int, char**)
         cap >> frame;
         cvtColor(frame, gray, COLOR_BGR2GRAY);
 
-        if( prevgray.data )
+        if( !prevgray.empty() )
         {
-            calcOpticalFlowFarneback(prevgray, gray, flow, 0.5, 3, 15, 3, 5, 1.2, 0);
+            calcOpticalFlowFarneback(prevgray, gray, uflow, 0.5, 3, 15, 3, 5, 1.2, 0);
             cvtColor(prevgray, cflow, COLOR_GRAY2BGR);
+            uflow.copyTo(flow);
             drawOptFlowMap(flow, cflow, 16, 1.5, Scalar(0, 255, 0));
             imshow("flow", cflow);
         }