diff --git a/modules/calib3d/src/fisheye.cpp b/modules/calib3d/src/fisheye.cpp
index 9882cd8792..a2f117b028 100644
--- a/modules/calib3d/src/fisheye.cpp
+++ b/modules/calib3d/src/fisheye.cpp
@@ -1028,8 +1028,10 @@ double cv::fisheye::stereoCalibrate(InputArrayOfArrays objectPoints, InputArrayO
         int a = cv::countNonZero(intrinsicLeft.isEstimate);
         int b = cv::countNonZero(intrinsicRight.isEstimate);
         cv::Mat deltas = J2_inv * J.t() * e;
-        intrinsicLeft = intrinsicLeft + deltas.rowRange(0, a);
-        intrinsicRight = intrinsicRight + deltas.rowRange(a, a + b);
+        if (a > 0)
+            intrinsicLeft = intrinsicLeft + deltas.rowRange(0, a);
+        if (b > 0)
+            intrinsicRight = intrinsicRight + deltas.rowRange(a, a + b);
         omcur = omcur + cv::Vec3d(deltas.rowRange(a + b, a + b + 3));
         Tcur = Tcur + cv::Vec3d(deltas.rowRange(a + b + 3, a + b + 6));
         for (int image_idx = 0; image_idx < n_images; ++image_idx)
diff --git a/modules/core/include/opencv2/core/mat.hpp b/modules/core/include/opencv2/core/mat.hpp
index 631c698081..bebe2262b2 100644
--- a/modules/core/include/opencv2/core/mat.hpp
+++ b/modules/core/include/opencv2/core/mat.hpp
@@ -368,6 +368,16 @@ inline void Mat::release()
     data = datastart = dataend = datalimit = 0;
     for(int i = 0; i < dims; i++)
         size.p[i] = 0;
+#ifdef _DEBUG
+    flags = MAGIC_VAL;
+    dims = rows = cols = 0;
+    if (step.p != step.buf)
+    {
+        fastFree(step.p);
+        step.p = step.buf;
+        size.p = &rows;
+    }
+#endif
     refcount = 0;
 }