diff --git a/modules/calib3d/src/ptsetreg.cpp b/modules/calib3d/src/ptsetreg.cpp
index f417696547..463027d510 100644
--- a/modules/calib3d/src/ptsetreg.cpp
+++ b/modules/calib3d/src/ptsetreg.cpp
@@ -462,7 +462,7 @@ public:
             double b = F[4]*f.x + F[5]*f.y + F[ 6]*f.z + F[ 7] - t.y;
             double c = F[8]*f.x + F[9]*f.y + F[10]*f.z + F[11] - t.z;
 
-            errptr[i] = (float)std::sqrt(a*a + b*b + c*c);
+            errptr[i] = (float)(a*a + b*b + c*c);
         }
     }
 
diff --git a/modules/core/test/test_math.cpp b/modules/core/test/test_math.cpp
index 288c0c1f48..5eb9fe267f 100644
--- a/modules/core/test/test_math.cpp
+++ b/modules/core/test/test_math.cpp
@@ -2384,7 +2384,7 @@ TEST(Core_SolvePoly, regression_5599)
         double prec;
         prec = cv::solvePoly(coefs, r);
         EXPECT_LE(prec, 1e-6);
-        EXPECT_EQ(4, r.total());
+        EXPECT_EQ(4u, r.total());
         //std::cout << "Preciseness = " << prec << std::endl;
         //std::cout << "roots:\n" << r << "\n" << std::endl;
         ASSERT_EQ(CV_32FC2, r.type());
@@ -2400,7 +2400,7 @@ TEST(Core_SolvePoly, regression_5599)
         double prec;
         prec = cv::solvePoly(coefs, r);
         EXPECT_LE(prec, 1e-6);
-        EXPECT_EQ(2, r.total());
+        EXPECT_EQ(2u, r.total());
         //std::cout << "Preciseness = " << prec << std::endl;
         //std::cout << "roots:\n" << r << "\n" << std::endl;
         ASSERT_EQ(CV_32FC2, r.type());
diff --git a/modules/core/test/test_utils.cpp b/modules/core/test/test_utils.cpp
index a527ba6f28..8ff76af661 100644
--- a/modules/core/test/test_utils.cpp
+++ b/modules/core/test/test_utils.cpp
@@ -223,13 +223,13 @@ TEST(CommandLineParser, positional_regression_5074_equal_sign)
 TEST(AutoBuffer, allocate_test)
 {
     AutoBuffer<int, 5> abuf(2);
-    EXPECT_EQ(2, abuf.size());
+    EXPECT_EQ(2u, abuf.size());
 
     abuf.allocate(4);
-    EXPECT_EQ(4, abuf.size());
+    EXPECT_EQ(4u, abuf.size());
 
     abuf.allocate(6);
-    EXPECT_EQ(6, abuf.size());
+    EXPECT_EQ(6u, abuf.size());
 }
 
 } // namespace
diff --git a/modules/imgproc/src/color.cpp b/modules/imgproc/src/color.cpp
index cb71a13407..b08c608220 100644
--- a/modules/imgproc/src/color.cpp
+++ b/modules/imgproc/src/color.cpp
@@ -8394,7 +8394,11 @@ void cv::cvtColor( InputArray _src, OutputArray _dst, int code, int dcn )
     CV_OCL_RUN( _src.dims() <= 2 && _dst.isUMat() && !(depth == CV_8U && (code == CV_Luv2BGR || code == CV_Luv2RGB)),
                 ocl_cvtColor(_src, _dst, code, dcn) )
 
-    Mat src = _src.getMat(), dst;
+    Mat src, dst;
+    if (_src.getObj() == _dst.getObj()) // inplace processing (#6653)
+        _src.copyTo(src);
+    else
+        src = _src.getMat();
     Size sz = src.size();
     CV_Assert( depth == CV_8U || depth == CV_16U || depth == CV_32F );