diff --git a/src/resizable.cc b/src/resizable.cc
index 84751d1..9dfe92d 100644
--- a/src/resizable.cc
+++ b/src/resizable.cc
@@ -41,16 +41,18 @@ namespace php_arma
             Z_PARAM_ZVAL(other)
         ZEND_PARSE_PARAMETERS_END();
 
-        if (UNEXPECTED(Z_TYPE_P(other) != IS_OBJECT || instanceof_function(Z_OBJCE_P(other), base_ce))) {
+        if (UNEXPECTED(Z_TYPE_P(other) != IS_OBJECT || !instanceof_function(Z_OBJCE_P(other), base_ce))) {
             ex_bad_type(ZSTR_VAL(base_ce->name), zval_get_type_name(other));
             return;
         }
 
         std::variant<ds::base*, ds::subview*, ds::diagview*> other_native_v;
-        if (instanceof_function(Z_OBJCE_P(other), diagonal_ce)) {
-            other_native_v = to_native_object<ds::diagview>(Z_OBJ_P(other));
-        } else if (instanceof_function(Z_OBJCE_P(other), subview_ce)) {
-            other_native_v = to_native_object<ds::subview>(Z_OBJ_P(other));
+        if (instanceof_function(Z_OBJCE_P(other), subview_ce)) {
+            if (instanceof_function(Z_OBJCE_P(other), diagonal_ce)) {
+                other_native_v = to_native_object<ds::diagview>(Z_OBJ_P(other));
+            } else {
+                other_native_v = to_native_object<ds::subview>(Z_OBJ_P(other));
+            }
         } else {
             other_native_v = to_native_object<ds::base>(Z_OBJ_P(other));
         }
diff --git a/tests/020-copy-size.phpt b/tests/020-copy-size.phpt
new file mode 100644
index 0000000..836df3c
--- /dev/null
+++ b/tests/020-copy-size.phpt
@@ -0,0 +1,25 @@
+--TEST--
+Test for method `copySize()`
+--SKIPIF--
+<?php
+require_once 'includes/loaded.php';
+is_php_arma_loaded();
+?>
+--FILE--
+<?php
+
+require_once 'includes/assert.php';
+
+$imat = Arma\IMat::init(3, 3);
+$dmat = Arma\DMat::init(2, 5);
+$dmat->copySize($dmat->submat(0, 1, 1, 3));
+$imat->copySize($imat->diag());
+batch_assert('method `copySize()`',
+    [$dmat->nRows(), 2],
+    [$dmat->nCols(), 3],
+    [$imat->nRows(), 3],
+    [$imat->nCols(), 1]
+);
+
+?>
+--EXPECT--