diff --git a/src/Magnum/Trade/AbstractSceneConverter.cpp b/src/Magnum/Trade/AbstractSceneConverter.cpp
index fe968e56d..85ff16469 100644
--- a/src/Magnum/Trade/AbstractSceneConverter.cpp
+++ b/src/Magnum/Trade/AbstractSceneConverter.cpp
@@ -1296,8 +1296,6 @@ Containers::Optional<UnsignedInt> AbstractSceneConverter::add(const Containers::
 bool AbstractSceneConverter::addImporterContentsInternal(AbstractImporter& importer, const SceneContents contents, const bool noLevelsIfUnsupported) {
     CORRADE_ASSERT(isConverting(),
         "Trade::AbstractSceneConverter::addImporterContents(): no conversion in progress", {});
-    CORRADE_ASSERT(importer.isOpened(),
-        "Trade::AbstractSceneConverter::addImporterContents(): the importer is not opened", {});
     const SceneContents contentsSupported = sceneContentsFor(*this);
     #ifndef CORRADE_NO_ASSERT
     const SceneContents contentsPresentExceptLevels = contents & sceneContentsFor(importer);
@@ -1640,10 +1638,15 @@ bool AbstractSceneConverter::addImporterContentsInternal(AbstractImporter& impor
 
 
 bool AbstractSceneConverter::addImporterContents(AbstractImporter& importer, const SceneContents contents) {
+    CORRADE_ASSERT(importer.isOpened(),
+        "Trade::AbstractSceneConverter::addImporterContents(): the importer is not opened", {});
     return addImporterContentsInternal(importer, contents, false);
 }
 
 bool AbstractSceneConverter::addSupportedImporterContents(AbstractImporter& importer, const SceneContents contents) {
+    CORRADE_ASSERT(importer.isOpened(),
+        "Trade::AbstractSceneConverter::addSupportedImporterContents(): the importer is not opened", {});
+
     /* To avoid accidental differences in handling SceneConverterFeatures in
        sceneContentsFor(const AbstractSceneConverter&) and here, this branches
        on SceneContents instead of SceneConverterFeatures */
diff --git a/src/Magnum/Trade/Test/AbstractSceneConverterTest.cpp b/src/Magnum/Trade/Test/AbstractSceneConverterTest.cpp
index f494918ef..6bb9c5207 100644
--- a/src/Magnum/Trade/Test/AbstractSceneConverterTest.cpp
+++ b/src/Magnum/Trade/Test/AbstractSceneConverterTest.cpp
@@ -302,6 +302,7 @@ struct AbstractSceneConverterTest: TestSuite::Tester {
 
     void addSupportedImporterContents();
     void addSupportedImporterContentsLevels();
+    void addSupportedImporterContentsNotOpened();
 
     void debugFeature();
     void debugFeaturePacked();
@@ -864,7 +865,8 @@ AbstractSceneConverterTest::AbstractSceneConverterTest() {
     addInstancedTests({&AbstractSceneConverterTest::addSupportedImporterContents},
         Containers::arraySize(AddSupportedImporterContentsData));
 
-    addTests({&AbstractSceneConverterTest::addSupportedImporterContentsLevels,
+    addTests({&AbstractSceneConverterTest::addSupportedImporterContentsNotOpened,
+              &AbstractSceneConverterTest::addSupportedImporterContentsLevels,
 
               &AbstractSceneConverterTest::debugFeature,
               &AbstractSceneConverterTest::debugFeaturePacked,
@@ -7505,6 +7507,30 @@ void AbstractSceneConverterTest::addSupportedImporterContentsLevels() {
     CORRADE_COMPARE(converter.image3DCount(), importer.image3DCount());
 }
 
+void AbstractSceneConverterTest::addSupportedImporterContentsNotOpened() {
+    CORRADE_SKIP_IF_NO_ASSERT();
+
+    struct: AbstractImporter {
+        ImporterFeatures doFeatures() const override { return {}; }
+        bool doIsOpened() const override { return false; }
+        void doClose() override {}
+    } importer;
+
+    struct: AbstractSceneConverter {
+        SceneConverterFeatures doFeatures() const override {
+            return SceneConverterFeature::ConvertMultipleToData;
+        }
+        bool doBeginData() override { return true; }
+    } converter;
+
+    CORRADE_VERIFY(converter.beginData());
+
+    std::ostringstream out;
+    Error redirectError{&out};
+    CORRADE_VERIFY(!converter.addSupportedImporterContents(importer));
+    CORRADE_COMPARE(out.str(), "Trade::AbstractSceneConverter::addSupportedImporterContents(): the importer is not opened\n");
+}
+
 void AbstractSceneConverterTest::debugFeature() {
     std::ostringstream out;