diff --git a/modules/core/src/mathfuncs_core.simd.hpp b/modules/core/src/mathfuncs_core.simd.hpp
index 8c4dbffe1d..ec0e948f3f 100644
--- a/modules/core/src/mathfuncs_core.simd.hpp
+++ b/modules/core/src/mathfuncs_core.simd.hpp
@@ -119,7 +119,7 @@ static void cartToPolar32f_(const float *X, const float *Y, float *mag, float *a
             // if it's inplace operation, we cannot repeatedly process
             // the tail for the second time, so we have to use the
             // scalar code
-            if( i == 0 || angle == X || angle == Y )
+            if( i == 0 || mag == X || mag == Y || angle == X || angle == Y )
                 break;
             i = len - VECSZ*2;
         }
diff --git a/modules/core/test/test_arithm.cpp b/modules/core/test/test_arithm.cpp
index 9da3f03586..ec120816ab 100644
--- a/modules/core/test/test_arithm.cpp
+++ b/modules/core/test/test_arithm.cpp
@@ -3358,6 +3358,35 @@ INSTANTIATE_TEST_CASE_P(Core_CartPolar, Core_CartToPolar_inplace,
     )
 );
 
+typedef testing::TestWithParam<int> Core_CartToPolar_inplace_mag;
+
+// only the magnitude overwrites an input, so the last elements must not be processed twice.
+// CV_64F is not tested: it works on separate float buffers, so it can't hit this.
+TEST_P(Core_CartToPolar_inplace_mag, accuracy)
+{
+    const int len = GetParam();
+    cv::Mat x(1, len, CV_32F), y(1, len, CV_32F);
+    cv::randu(x, cv::Scalar::all(-1000), cv::Scalar::all(1000));
+    cv::randu(y, cv::Scalar::all(-1000), cv::Scalar::all(1000));
+
+    cv::Mat expectedMag, expectedAngle;
+    cv::cartToPolar(x, y, expectedMag, expectedAngle);
+
+    // magnitude into x
+    cv::Mat x1 = x.clone(), angle1;
+    cv::cartToPolar(x1, y, x1, angle1);
+    EXPECT_MAT_NEAR(expectedMag, x1, 1e-2);
+    EXPECT_MAT_NEAR(expectedAngle, angle1, 1e-2);
+
+    // magnitude into y
+    cv::Mat y1 = y.clone(), angle2;
+    cv::cartToPolar(x, y1, y1, angle2);
+    EXPECT_MAT_NEAR(expectedMag, y1, 1e-2);
+    EXPECT_MAT_NEAR(expectedAngle, angle2, 1e-2);
+}
+
+INSTANTIATE_TEST_CASE_P(Core_CartPolar, Core_CartToPolar_inplace_mag, testing::Range(1, 40));
+
 PARAM_TEST_CASE(Core_PolarToCart_inplace, int, bool, bool)
 {
     int  depth;