diff --git a/src/Magnum/MeshTools/Duplicate.cpp b/src/Magnum/MeshTools/Duplicate.cpp
index 7ba68fe30..7e4fcb997 100644
--- a/src/Magnum/MeshTools/Duplicate.cpp
+++ b/src/Magnum/MeshTools/Duplicate.cpp
@@ -80,6 +80,20 @@ void duplicateInto(const Containers::StridedArrayView2D<const char>& indices, co
 
 Trade::MeshData duplicate(const Trade::MeshData& data, const Containers::ArrayView<const Trade::MeshAttributeData> extra) {
     CORRADE_ASSERT(data.isIndexed(), "MeshTools::duplicate(): mesh data not indexed", (Trade::MeshData{MeshPrimitive::Triangles, 0}));
+    #ifndef CORRADE_NO_ASSERT
+    for(std::size_t i = 0; i != data.attributeCount(); ++i) {
+        const VertexFormat format = data.attributeFormat(i);
+        CORRADE_ASSERT(!isVertexFormatImplementationSpecific(format),
+            "MeshTools::duplicate(): attribute" << i << "has an implementation-specific format" << reinterpret_cast<void*>(vertexFormatUnwrap(format)),
+            (Trade::MeshData{MeshPrimitive::Points, 0}));
+    }
+    for(std::size_t i = 0; i != extra.size(); ++i) {
+        const VertexFormat format = extra[i].format();
+        CORRADE_ASSERT(!isVertexFormatImplementationSpecific(format),
+            "MeshTools::duplicate(): extra attribute" << i << "has an implementation-specific format" << reinterpret_cast<void*>(vertexFormatUnwrap(format)),
+            (Trade::MeshData{MeshPrimitive::Points, 0}));
+    }
+    #endif
 
     /* Calculate the layout */
     Trade::MeshData layout = interleavedLayout(data, data.indexCount(), extra);
diff --git a/src/Magnum/MeshTools/Duplicate.h b/src/Magnum/MeshTools/Duplicate.h
index bb537e3f5..7a1e7a808 100644
--- a/src/Magnum/MeshTools/Duplicate.h
+++ b/src/Magnum/MeshTools/Duplicate.h
@@ -146,8 +146,10 @@ instances are not supported in the @p extra array.
 
 Expects that @p data is indexed and each attribute in @p extra has either the
 same amount of elements as @p data vertex count (*not* index count) or has
-none.
-@see @ref Trade::MeshData::attributeData()
+none. All attributes are expected to not have an implementation-specific
+format.
+@see @ref isVertexFormatImplementationSpecific(),
+    @ref Trade::MeshData::attributeData()
 */
 MAGNUM_MESHTOOLS_EXPORT Trade::MeshData duplicate(const Trade::MeshData& data, Containers::ArrayView<const Trade::MeshAttributeData> extra = {});
 
diff --git a/src/Magnum/MeshTools/Test/DuplicateTest.cpp b/src/Magnum/MeshTools/Test/DuplicateTest.cpp
index 108128e9f..1b53ebe00 100644
--- a/src/Magnum/MeshTools/Test/DuplicateTest.cpp
+++ b/src/Magnum/MeshTools/Test/DuplicateTest.cpp
@@ -59,10 +59,12 @@ struct DuplicateTest: TestSuite::Tester {
 
     template<class T> void duplicateMeshData();
     void duplicateMeshDataNotIndexed();
+    void duplicateMeshDataImplementationSpecificVertexFormat();
     void duplicateMeshDataExtra();
     void duplicateMeshDataExtraEmpty();
     void duplicateMeshDataExtraWrongCount();
     void duplicateMeshDataExtraOffsetOnly();
+    void duplicateMeshDataExtraImplementationSpecificVertexFormat();
     void duplicateMeshDataNoAttributes();
 };
 
@@ -92,10 +94,12 @@ DuplicateTest::DuplicateTest() {
               &DuplicateTest::duplicateMeshData<UnsignedShort>,
               &DuplicateTest::duplicateMeshData<UnsignedInt>,
               &DuplicateTest::duplicateMeshDataNotIndexed,
+              &DuplicateTest::duplicateMeshDataImplementationSpecificVertexFormat,
               &DuplicateTest::duplicateMeshDataExtra,
               &DuplicateTest::duplicateMeshDataExtraEmpty,
               &DuplicateTest::duplicateMeshDataExtraWrongCount,
               &DuplicateTest::duplicateMeshDataExtraOffsetOnly,
+              &DuplicateTest::duplicateMeshDataExtraImplementationSpecificVertexFormat,
               &DuplicateTest::duplicateMeshDataNoAttributes});
 }
 
@@ -326,6 +330,28 @@ void DuplicateTest::duplicateMeshDataNotIndexed() {
     CORRADE_COMPARE(out.str(), "MeshTools::duplicate(): mesh data not indexed\n");
 }
 
+void DuplicateTest::duplicateMeshDataImplementationSpecificVertexFormat() {
+    #ifdef CORRADE_NO_ASSERT
+    CORRADE_SKIP("CORRADE_NO_ASSERT defined, can't test assertions");
+    #endif
+
+    Trade::MeshData a{MeshPrimitive::Lines,
+        nullptr, Trade::MeshIndexData{MeshIndexType::UnsignedShort, nullptr},
+        nullptr, {
+        Trade::MeshAttributeData{Trade::MeshAttribute::Position,
+            VertexFormat::Vector3, nullptr},
+        Trade::MeshAttributeData{Trade::MeshAttribute::Position,
+            VertexFormat::Vector3, nullptr},
+        Trade::MeshAttributeData{Trade::MeshAttribute::Color,
+            vertexFormatWrap(0xcaca), nullptr}
+    }};
+
+    std::ostringstream out;
+    Error redirectError{&out};
+    MeshTools::duplicate(a);
+    CORRADE_COMPARE(out.str(), "MeshTools::duplicate(): attribute 2 has an implementation-specific format 0xcaca\n");
+}
+
 void DuplicateTest::duplicateMeshDataExtra() {
     UnsignedByte indices[]{0, 1, 2, 2, 1, 0};
     Vector2 positions[]{{1.3f, 0.3f}, {0.87f, 1.1f}, {1.0f, -0.5f}};
@@ -431,6 +457,29 @@ void DuplicateTest::duplicateMeshDataExtraOffsetOnly() {
     CORRADE_COMPARE(out.str(), "MeshTools::duplicate(): extra attribute 1 is offset-only, which is not supported\n");
 }
 
+void DuplicateTest::duplicateMeshDataExtraImplementationSpecificVertexFormat() {
+    #ifdef CORRADE_NO_ASSERT
+    CORRADE_SKIP("CORRADE_NO_ASSERT defined, can't test assertions");
+    #endif
+
+    Trade::MeshData a{MeshPrimitive::Lines,
+        nullptr, Trade::MeshIndexData{MeshIndexType::UnsignedShort, nullptr},
+        nullptr, {
+        Trade::MeshAttributeData{Trade::MeshAttribute::Position,
+            VertexFormat::Vector3, nullptr},
+    }};
+
+    std::ostringstream out;
+    Error redirectError{&out};
+    MeshTools::duplicate(a, {
+        Trade::MeshAttributeData{Trade::MeshAttribute::Position,
+            VertexFormat::Vector3, nullptr},
+        Trade::MeshAttributeData{Trade::MeshAttribute::Color,
+            vertexFormatWrap(0xcaca), nullptr}
+    });
+    CORRADE_COMPARE(out.str(), "MeshTools::duplicate(): extra attribute 1 has an implementation-specific format 0xcaca\n");
+}
+
 void DuplicateTest::duplicateMeshDataNoAttributes() {
     UnsignedByte indices[]{0, 1, 2, 2, 1, 0};
     Trade::MeshData data{MeshPrimitive::Lines,