diff --git a/modules/core/src/matrix.cpp b/modules/core/src/matrix.cpp
index 995c10b5be..07da4ad724 100644
--- a/modules/core/src/matrix.cpp
+++ b/modules/core/src/matrix.cpp
@@ -126,7 +126,7 @@ void MatAllocator::upload(UMatData* u, const void* srcptr, int dims, const size_
 
 void MatAllocator::copy(UMatData* usrc, UMatData* udst, int dims, const size_t sz[],
                   const size_t srcofs[], const size_t srcstep[],
-                  const size_t dstofs[], const size_t dststep[], bool sync) const
+                  const size_t dstofs[], const size_t dststep[], bool /*sync*/) const
 {
     if(!usrc || !udst)
         return;
diff --git a/modules/core/src/ocl.cpp b/modules/core/src/ocl.cpp
index 22d8022439..9032546e40 100644
--- a/modules/core/src/ocl.cpp
+++ b/modules/core/src/ocl.cpp
@@ -2258,25 +2258,21 @@ bool Kernel::run(int dims, size_t _globalsize[], size_t _localsize[],
         return false;
 
     cl_command_queue qq = getQueue(q);
-    size_t offset[CV_MAX_DIM] = {0}, globalsize[CV_MAX_DIM] = {1,1,1}, localsize[CV_MAX_DIM] = {1,1,1};
+    size_t offset[CV_MAX_DIM] = {0}, globalsize[CV_MAX_DIM] = {1,1,1};
     size_t total = 1;
+    CV_Assert(_globalsize != 0);
     for (int i = 0; i < dims; i++)
     {
-        size_t val0 = _localsize ? _localsize[i] :
-            dims == 1 ? 64 : dims == 2 ? 16>>i : dims == 3 ? 8>>(i>0) : 1;
-        size_t val = 1;
-        while( val*2 < val0 )
-            val *= 2;
-        if( _localsize )
-            localsize[i] = val;
-        CV_Assert(_globalsize && _globalsize[i] >= 0);
+        size_t val = _localsize ? _localsize[i] :
+            dims == 1 ? 64 : dims == 2 ? (16>>i) : dims == 3 ? (8>>(int)(i>0)) : 1;
+        CV_Assert( val > 0 );
         total *= _globalsize[i];
         globalsize[i] = ((_globalsize[i] + val - 1)/val)*val;
     }
     if( total == 0 )
         return true;
     cl_int retval = clEnqueueNDRangeKernel(qq, p->handle, (cl_uint)dims,
-                                           offset, globalsize, _localsize ? localsize : 0, 0, 0,
+                                           offset, globalsize, _localsize, 0, 0,
                                            sync ? 0 : &p->e);
     if( sync || retval < 0 )
     {
@@ -2976,7 +2972,7 @@ public:
             return;
 
         // there should be no user-visible CPU copies of the UMat which we are going to copy to
-        CV_Assert(u->refcount == 0);
+        CV_Assert(u->refcount == 0 || u->tempUMat());
 
         size_t total = 0, new_sz[] = {0, 0, 0};
         size_t srcrawofs = 0, new_srcofs[] = {0, 0, 0}, new_srcstep[] = {0, 0, 0};
@@ -3028,7 +3024,7 @@ public:
 
     void copy(UMatData* src, UMatData* dst, int dims, const size_t sz[],
               const size_t srcofs[], const size_t srcstep[],
-              const size_t dstofs[], const size_t dststep[], bool sync) const
+              const size_t dstofs[], const size_t dststep[], bool _sync) const
     {
         if(!src || !dst)
             return;
@@ -3072,14 +3068,15 @@ public:
             cl_int retval;
             CV_Assert( (retval = clEnqueueCopyBufferRect(q, (cl_mem)src->handle, (cl_mem)dst->handle,
                                                new_srcofs, new_dstofs, new_sz,
-                                               new_srcstep[0], new_srcstep[1], new_dststep[0], new_dststep[1],
+                                               new_srcstep[0], new_srcstep[1],
+                                               new_dststep[0], new_dststep[1],
                                                0, 0, 0)) >= 0 );
         }
 
         dst->markHostCopyObsolete(true);
         dst->markDeviceCopyObsolete(false);
 
-        if( sync )
+        if( _sync )
             clFinish(q);
     }
 
diff --git a/modules/core/test/test_umat.cpp b/modules/core/test/test_umat.cpp
index 54df893bfe..7cd523d85c 100644
--- a/modules/core/test/test_umat.cpp
+++ b/modules/core/test/test_umat.cpp
@@ -201,7 +201,7 @@ void CV_UMatTest::run( int /* start_from */)
 
 TEST(Core_UMat, base) { CV_UMatTest test; test.safe_run(); }
 
-TEST(Core_UMat, simple)
+TEST(Core_UMat, getUMat)
 {
     {
     int a[3] = { 1, 2, 3 };
@@ -216,7 +216,7 @@ TEST(Core_UMat, simple)
     {
         uchar * const ptr = m.ptr<uchar>(y);
         for (int x = 0; x < m.cols; ++x)
-            ptr[x] = x + y * 2;
+            ptr[x] = (uchar)(x + y * 2);
     }
 
     ref = m.clone();
diff --git a/modules/imgproc/src/opencl/cvtcolor.cl b/modules/imgproc/src/opencl/cvtcolor.cl
index 85c0ca6e34..883e2eb4d4 100644
--- a/modules/imgproc/src/opencl/cvtcolor.cl
+++ b/modules/imgproc/src/opencl/cvtcolor.cl
@@ -124,16 +124,17 @@ __kernel void RGB2Gray(__global const uchar* srcptr, int srcstep, int srcoffset,
 #endif
     }
 #else
-    const int x0 = get_global_id(0)*STRIPE_SIZE;
-    const int x1 = min(x0 + STRIPE_SIZE, cols);
+    const int x_min = get_global_id(0)*STRIPE_SIZE;
+    const int x_max = min(x_min + STRIPE_SIZE, cols);
     const int y = get_global_id(1);
 
     if( y < rows )
     {
-        __global const DATA_TYPE* src = (__global const DATA_TYPE*)(srcptr + mad24(y, srcstep, srcoffset)) + x0*scn;
+        __global const DATA_TYPE* src = (__global const DATA_TYPE*)(srcptr +
+                                        mad24(y, srcstep, srcoffset)) + x_min*scn;
         __global DATA_TYPE* dst = (__global DATA_TYPE*)(dstptr + mad24(y, dststep, dstoffset));
         int x;
-        for( x = x0; x < x1; x++, src += scn )
+        for( x = x_min; x < x_max; x++, src += scn )
 #ifdef DEPTH_5
         dst[x] = src[bidx] * 0.114f + src[1] * 0.587f + src[(bidx^2)] * 0.299f;
 #else
diff --git a/modules/ocl/test/test_api.cpp b/modules/ocl/test/test_api.cpp
index a95e60e65c..68888a7c08 100644
--- a/modules/ocl/test/test_api.cpp
+++ b/modules/ocl/test/test_api.cpp
@@ -136,4 +136,3 @@ TEST(OCL_TestTAPI, performance)
     cv::destroyWindow("result0");
     cv::destroyWindow("result1");*/
 }
-