diff --git a/doc/python/magnum.trade.rst b/doc/python/magnum.trade.rst
index c6bb0d2..b9a628f 100644
--- a/doc/python/magnum.trade.rst
+++ b/doc/python/magnum.trade.rst
@@ -97,68 +97,72 @@
     :raise RuntimeError: If file opening fails
 
 .. py:property:: magnum.trade.AbstractImporter.mesh_count
-    :raise RuntimeError: If no file is opened
+    :raise AssertionError: If no file is opened
 .. py:function:: magnum.trade.AbstractImporter.mesh_level_count
-    :raise RuntimeError: If no file is opened
-    :raise ValueError: If :p:`id` is negative or not less than :ref:`mesh_count`
+    :raise AssertionError: If no file is opened
+    :raise IndexError: If :p:`id` is negative or not less than :ref:`mesh_count`
 .. py:function:: magnum.trade.AbstractImporter.mesh_for_name
-    :raise RuntimeError: If no file is opened
+    :raise AssertionError: If no file is opened
 .. py:function:: magnum.trade.AbstractImporter.mesh_name
-    :raise RuntimeError: If no file is opened
-    :raise ValueError: If :p:`id` is negative or not less than :ref:`mesh_count`
+    :raise AssertionError: If no file is opened
+    :raise IndexError: If :p:`id` is negative or not less than :ref:`mesh_count`
 .. py:function:: magnum.trade.AbstractImporter.mesh
-    :raise RuntimeError: If no file is opened
-    :raise ValueError: If :p:`id` is negative or not less than :ref:`mesh_count`
+    :raise AssertionError: If no file is opened
+    :raise RuntimeError: If mesh import fails
+    :raise IndexError: If :p:`id` is negative or not less than :ref:`mesh_count`
 
 .. py:property:: magnum.trade.AbstractImporter.image1d_count
-    :raise RuntimeError: If no file is opened
+    :raise AssertionError: If no file is opened
 .. py:property:: magnum.trade.AbstractImporter.image2d_count
-    :raise RuntimeError: If no file is opened
+    :raise AssertionError: If no file is opened
 .. py:property:: magnum.trade.AbstractImporter.image3d_count
-    :raise RuntimeError: If no file is opened
+    :raise AssertionError: If no file is opened
 
 .. py:function:: magnum.trade.AbstractImporter.image1d_level_count
-    :raise RuntimeError: If no file is opened
-    :raise ValueError: If :p:`id` is negative or not less than
+    :raise AssertionError: If no file is opened
+    :raise IndexError: If :p:`id` is negative or not less than
         :ref:`image1d_count`
 .. py:function:: magnum.trade.AbstractImporter.image2d_level_count
-    :raise RuntimeError: If no file is opened
-    :raise ValueError: If :p:`id` is negative or not less than
+    :raise AssertionError: If no file is opened
+    :raise IndexError: If :p:`id` is negative or not less than
         :ref:`image2d_count`
 .. py:function:: magnum.trade.AbstractImporter.image3d_level_count
-    :raise RuntimeError: If no file is opened
-    :raise ValueError: If :p:`id` is negative or not less than
+    :raise AssertionError: If no file is opened
+    :raise IndexError: If :p:`id` is negative or not less than
         :ref:`image3d_count`
 
 .. py:function:: magnum.trade.AbstractImporter.image1d_for_name
-    :raise RuntimeError: If no file is opened
+    :raise AssertionError: If no file is opened
 .. py:function:: magnum.trade.AbstractImporter.image2d_for_name
-    :raise RuntimeError: If no file is opened
+    :raise AssertionError: If no file is opened
 .. py:function:: magnum.trade.AbstractImporter.image3d_for_name
-    :raise RuntimeError: If no file is opened
+    :raise AssertionError: If no file is opened
 
 .. py:function:: magnum.trade.AbstractImporter.image1d_name
-    :raise RuntimeError: If no file is opened
-    :raise ValueError: If :p:`id` is negative or not less than
+    :raise AssertionError: If no file is opened
+    :raise IndexError: If :p:`id` is negative or not less than
         :ref:`image1d_count`
 .. py:function:: magnum.trade.AbstractImporter.image2d_name
-    :raise RuntimeError: If no file is opened
-    :raise ValueError: If :p:`id` is negative or not less than
+    :raise AssertionError: If no file is opened
+    :raise IndexError: If :p:`id` is negative or not less than
         :ref:`image2d_count`
 .. py:function:: magnum.trade.AbstractImporter.image3d_name
-    :raise RuntimeError: If no file is opened
-    :raise ValueError: If :p:`id` is negative or not less than
+    :raise AssertionError: If no file is opened
+    :raise IndexError: If :p:`id` is negative or not less than
         :ref:`image3d_count`
 
 .. py:function:: magnum.trade.AbstractImporter.image1d
-    :raise RuntimeError: If no file is opened
-    :raise ValueError: If :p:`id` is negative or not less than
+    :raise AssertionError: If no file is opened
+    :raise RuntimeError: If image import fails
+    :raise IndexError: If :p:`id` is negative or not less than
         :ref:`image1d_count`
 .. py:function:: magnum.trade.AbstractImporter.image2d
-    :raise RuntimeError: If no file is opened
-    :raise ValueError: If :p:`id` is negative or not less than
+    :raise AssertionError: If no file is opened
+    :raise RuntimeError: If image import fails
+    :raise IndexError: If :p:`id` is negative or not less than
         :ref:`image2d_count`
 .. py:function:: magnum.trade.AbstractImporter.image3d
-    :raise RuntimeError: If no file is opened
-    :raise ValueError: If :p:`id` is negative or not less than
+    :raise AssertionError: If no file is opened
+    :raise RuntimeError: If image import fails
+    :raise IndexError: If :p:`id` is negative or not less than
         :ref:`image3d_count`
diff --git a/src/python/magnum/test/test_trade.py b/src/python/magnum/test/test_trade.py
index f6e8bc5..683b96f 100644
--- a/src/python/magnum/test/test_trade.py
+++ b/src/python/magnum/test/test_trade.py
@@ -116,53 +116,53 @@ class Importer(unittest.TestCase):
         importer = trade.ImporterManager().load_and_instantiate('StbImageImporter')
         self.assertFalse(importer.is_opened)
 
-        with self.assertRaisesRegex(RuntimeError, "no file opened"):
+        with self.assertRaisesRegex(AssertionError, "no file opened"):
             importer.mesh_count
-        with self.assertRaisesRegex(RuntimeError, "no file opened"):
+        with self.assertRaisesRegex(AssertionError, "no file opened"):
             importer.mesh_level_count(0)
 
-        with self.assertRaisesRegex(RuntimeError, "no file opened"):
+        with self.assertRaisesRegex(AssertionError, "no file opened"):
             importer.mesh_for_name('')
 
-        with self.assertRaisesRegex(RuntimeError, "no file opened"):
+        with self.assertRaisesRegex(AssertionError, "no file opened"):
             importer.mesh_name(0)
 
-        with self.assertRaisesRegex(RuntimeError, "no file opened"):
+        with self.assertRaisesRegex(AssertionError, "no file opened"):
             importer.mesh(0)
 
-        with self.assertRaisesRegex(RuntimeError, "no file opened"):
+        with self.assertRaisesRegex(AssertionError, "no file opened"):
             importer.image1d_count
-        with self.assertRaisesRegex(RuntimeError, "no file opened"):
+        with self.assertRaisesRegex(AssertionError, "no file opened"):
             importer.image2d_count
-        with self.assertRaisesRegex(RuntimeError, "no file opened"):
+        with self.assertRaisesRegex(AssertionError, "no file opened"):
             importer.image3d_count
 
-        with self.assertRaisesRegex(RuntimeError, "no file opened"):
+        with self.assertRaisesRegex(AssertionError, "no file opened"):
             importer.image1d_level_count(0)
-        with self.assertRaisesRegex(RuntimeError, "no file opened"):
+        with self.assertRaisesRegex(AssertionError, "no file opened"):
             importer.image2d_level_count(0)
-        with self.assertRaisesRegex(RuntimeError, "no file opened"):
+        with self.assertRaisesRegex(AssertionError, "no file opened"):
             importer.image3d_level_count(0)
 
-        with self.assertRaisesRegex(RuntimeError, "no file opened"):
+        with self.assertRaisesRegex(AssertionError, "no file opened"):
             importer.image1d_for_name('')
-        with self.assertRaisesRegex(RuntimeError, "no file opened"):
+        with self.assertRaisesRegex(AssertionError, "no file opened"):
             importer.image2d_for_name('')
-        with self.assertRaisesRegex(RuntimeError, "no file opened"):
+        with self.assertRaisesRegex(AssertionError, "no file opened"):
             importer.image3d_for_name('')
 
-        with self.assertRaisesRegex(RuntimeError, "no file opened"):
+        with self.assertRaisesRegex(AssertionError, "no file opened"):
             importer.image1d_name(0)
-        with self.assertRaisesRegex(RuntimeError, "no file opened"):
+        with self.assertRaisesRegex(AssertionError, "no file opened"):
             importer.image2d_name(0)
-        with self.assertRaisesRegex(RuntimeError, "no file opened"):
+        with self.assertRaisesRegex(AssertionError, "no file opened"):
             importer.image3d_name(0)
 
-        with self.assertRaisesRegex(RuntimeError, "no file opened"):
+        with self.assertRaisesRegex(AssertionError, "no file opened"):
             importer.image1d(0)
-        with self.assertRaisesRegex(RuntimeError, "no file opened"):
+        with self.assertRaisesRegex(AssertionError, "no file opened"):
             importer.image2d(0)
-        with self.assertRaisesRegex(RuntimeError, "no file opened"):
+        with self.assertRaisesRegex(AssertionError, "no file opened"):
             importer.image3d(0)
 
     def test_index_oob(self):
diff --git a/src/python/magnum/trade.cpp b/src/python/magnum/trade.cpp
index 6761ce1..33a194b 100644
--- a/src/python/magnum/trade.cpp
+++ b/src/python/magnum/trade.cpp
@@ -143,14 +143,14 @@ template<UnsignedInt dimensions> void imageData(py::class_<Trade::ImageData<dime
    exactly two, in fact. */
 template<class R, R(Trade::AbstractImporter::*f)() const> R checkOpened(Trade::AbstractImporter& self) {
     if(!self.isOpened()) {
-        PyErr_SetString(PyExc_RuntimeError, "no file opened");
+        PyErr_SetString(PyExc_AssertionError, "no file opened");
         throw py::error_already_set{};
     }
     return (self.*f)();
 }
 template<class R, class Arg1, R(Trade::AbstractImporter::*f)(Arg1)> R checkOpened(Trade::AbstractImporter& self, Arg1 arg1) {
     if(!self.isOpened()) {
-        PyErr_SetString(PyExc_RuntimeError, "no file opened");
+        PyErr_SetString(PyExc_AssertionError, "no file opened");
         throw py::error_already_set{};
     }
     return (self.*f)(arg1);
@@ -158,7 +158,7 @@ template<class R, class Arg1, R(Trade::AbstractImporter::*f)(Arg1)> R checkOpene
 /** @todo drop this in favor of our own string caster */
 template<class R, R(Trade::AbstractImporter::*f)(Containers::StringView)> R checkOpenedString(Trade::AbstractImporter& self, const std::string& arg1) {
     if(!self.isOpened()) {
-        PyErr_SetString(PyExc_RuntimeError, "no file opened");
+        PyErr_SetString(PyExc_AssertionError, "no file opened");
         throw py::error_already_set{};
     }
     return (self.*f)(arg1);
@@ -166,7 +166,7 @@ template<class R, R(Trade::AbstractImporter::*f)(Containers::StringView)> R chec
 
 template<class R, R(Trade::AbstractImporter::*f)(UnsignedInt), UnsignedInt(Trade::AbstractImporter::*bounds)() const> R checkOpenedBounds(Trade::AbstractImporter& self, UnsignedInt id) {
     if(!self.isOpened()) {
-        PyErr_SetString(PyExc_RuntimeError, "no file opened");
+        PyErr_SetString(PyExc_AssertionError, "no file opened");
         throw py::error_already_set{};
     }
 
@@ -180,7 +180,7 @@ template<class R, R(Trade::AbstractImporter::*f)(UnsignedInt), UnsignedInt(Trade
 /** @todo drop this in favor of our own string caster */
 template<Containers::String(Trade::AbstractImporter::*f)(UnsignedInt), UnsignedInt(Trade::AbstractImporter::*bounds)() const> std::string checkOpenedBoundsReturnsString(Trade::AbstractImporter& self, UnsignedInt id) {
     if(!self.isOpened()) {
-        PyErr_SetString(PyExc_RuntimeError, "no file opened");
+        PyErr_SetString(PyExc_AssertionError, "no file opened");
         throw py::error_already_set{};
     }
 
@@ -194,7 +194,7 @@ template<Containers::String(Trade::AbstractImporter::*f)(UnsignedInt), UnsignedI
 
 template<class R, Containers::Optional<R>(Trade::AbstractImporter::*f)(UnsignedInt), UnsignedInt(Trade::AbstractImporter::*bounds)() const> R checkOpenedBoundsResult(Trade::AbstractImporter& self, UnsignedInt id) {
     if(!self.isOpened()) {
-        PyErr_SetString(PyExc_RuntimeError, "no file opened");
+        PyErr_SetString(PyExc_AssertionError, "no file opened");
         throw py::error_already_set{};
     }
 
@@ -216,7 +216,7 @@ template<class R, Containers::Optional<R>(Trade::AbstractImporter::*f)(UnsignedI
 
 template<class R, Containers::Optional<R>(Trade::AbstractImporter::*f)(UnsignedInt, UnsignedInt), UnsignedInt(Trade::AbstractImporter::*bounds)() const, UnsignedInt(Trade::AbstractImporter::*levelBounds)(UnsignedInt)> R checkOpenedBoundsResult(Trade::AbstractImporter& self, UnsignedInt id, UnsignedInt level) {
     if(!self.isOpened()) {
-        PyErr_SetString(PyExc_RuntimeError, "no file opened");
+        PyErr_SetString(PyExc_AssertionError, "no file opened");
         throw py::error_already_set{};
     }