diff --git a/src/ivoc/ocmatrix.cpp b/src/ivoc/ocmatrix.cpp
index b92cf39a78..123de08771 100644
--- a/src/ivoc/ocmatrix.cpp
+++ b/src/ivoc/ocmatrix.cpp
@@ -193,11 +193,13 @@ void OcFullMatrix::getdiag(int k, Vect* out) {
 #endif
         }
     } else {
+        // Yes for negative diagonal we set the vector from the middle
+        // The output vector should ALWAYS be the size of biggest diagonal
         for (i = -k, j = 0; i < row && j < col; ++i, ++j) {
 #ifdef WIN32
-            v_elem(out, j) = m_entry(m_, i, j);
+            v_elem(out, i) = m_entry(m_, i, j);
 #else
-            out->elem(j) = m_entry(m_, i, j);
+            out->elem(i) = m_entry(m_, i, j);
 #endif
         }
     }
@@ -228,11 +230,13 @@ void OcFullMatrix::setdiag(int k, Vect* in) {
 #endif
         }
     } else {
+        // Yes for negative diagonal we set the vector from the middle
+        // The input vector should ALWAYS be the size of biggest diagonal
         for (i = -k, j = 0; i < row && j < col; ++i, ++j) {
 #ifdef WIN32
-            m_set_val(m_, i, j, v_elem(in, j));
+            m_set_val(m_, i, j, v_elem(in, i));
 #else
-            m_set_val(m_, i, j, in->elem(j));
+            m_set_val(m_, i, j, in->elem(i));
 #endif
         }
     }
@@ -491,15 +495,17 @@ void OcSparseMatrix::setdiag(int k, Vect* in) {
         }
     } else {
         for (i = -k, j = 0; i < row && j < col; ++i, ++j) {
+            // Yes for negative diagonal we set the vector from the middle
+            // The input vector should ALWAYS be the size of biggest diagonal
             if ((p = pelm(i, j)) != nullptr) {
 #ifdef WIN32
-                *p = v_elem(in, j);
+                *p = v_elem(in, i);
             } else if (v_elem(in, i)) {
-                sp_set_val(m_, i, j, v_elem(in, j));
+                sp_set_val(m_, i, j, v_elem(in, i));
 #else
-                *p = in->elem(j);
+                *p = in->elem(i);
             } else if (in->elem(i)) {
-                sp_set_val(m_, i, j, in->elem(j));
+                sp_set_val(m_, i, j, in->elem(i));
 #endif
             }
         }
diff --git a/test/unit_tests/matrix.cpp b/test/unit_tests/matrix.cpp
index ebd487c391..fc91b654ca 100644
--- a/test/unit_tests/matrix.cpp
+++ b/test/unit_tests/matrix.cpp
@@ -192,16 +192,18 @@ SCENARIO("A Matrix", "[neuron_ivoc][OcMatrix]") {
             REQUIRE(compareMatrix(n, {{0., 0., 0.}, {0., 0., 0.}, {0., 0., 0.}}));
         }
         {
-            IvocVect v(2);
+            IvocVect v(3);
             m.getdiag(1, &v);
-            REQUIRE_THAT(v.vec(), Catch::Matchers::Approx(std::vector<double>({72., 114.})));
+            REQUIRE_THAT(v.vec(), Catch::Matchers::Approx(std::vector<double>({72., 114., 0.})));
+            v.vec() = {0., 72., 114.};
             m.setdiag(-1, &v);
             REQUIRE(compareMatrix(m, {{42., 72., 72.}, {72., 114., 114.}, {1., 114., 2.}}));
         }
         {
-            IvocVect v(1);
+            IvocVect v(3);
             m.getdiag(-2, &v);
-            REQUIRE_THAT(v.vec(), Catch::Matchers::Approx(std::vector<double>({1.})));
+            REQUIRE(v.vec()[2] == Catch::Detail::Approx({1.}));
+            v.vec() = {1., 0., 0.};
             m.setdiag(2, &v);
             REQUIRE(compareMatrix(m, {{42., 72., 1.}, {72., 114., 114.}, {1., 114., 2.}}));
         }
@@ -377,8 +379,8 @@ SCENARIO("A Matrix", "[neuron_ivoc][OcMatrix]") {
             REQUIRE(compareMatrix(m, {{1., 2., 3.}, {2., 2., 2.}, {3., 4., 3.}}));
         }
         {
-            IvocVect v(2);
-            v.vec() = {1, 2};
+            IvocVect v(3);
+            v.vec() = {0., 1., 2.};
             m.setdiag(-1, &v);
             REQUIRE(compareMatrix(m, {{1., 2., 3.}, {1., 2., 2.}, {3., 2., 3.}}));
         }