diff --git a/src/Magnum/MeshTools/Duplicate.cpp b/src/Magnum/MeshTools/Duplicate.cpp
index 7e4fcb997..36310e689 100644
--- a/src/Magnum/MeshTools/Duplicate.cpp
+++ b/src/Magnum/MeshTools/Duplicate.cpp
@@ -80,6 +80,9 @@ 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}));
+    CORRADE_ASSERT(!isMeshIndexTypeImplementationSpecific(data.indexType()),
+        "MeshTools::duplicate(): mesh has an implementation-specific index type" << reinterpret_cast<void*>(meshIndexTypeUnwrap(data.indexType())),
+        (Trade::MeshData{MeshPrimitive{}, 0}));
     #ifndef CORRADE_NO_ASSERT
     for(std::size_t i = 0; i != data.attributeCount(); ++i) {
         const VertexFormat format = data.attributeFormat(i);
diff --git a/src/Magnum/MeshTools/Duplicate.h b/src/Magnum/MeshTools/Duplicate.h
index 7a1e7a808..cf3b6ee3f 100644
--- a/src/Magnum/MeshTools/Duplicate.h
+++ b/src/Magnum/MeshTools/Duplicate.h
@@ -144,11 +144,12 @@ is done by @ref interleavedLayout(), see its documentation for detailed
 behavior description. Note that offset-only @ref Trade::MeshAttributeData
 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. All attributes are expected to not have an implementation-specific
-format.
-@see @ref isVertexFormatImplementationSpecific(),
+Expects that @p data is indexed with a non-implementation-specific index type
+and each attribute in @p extra has either the same amount of elements as
+@p data vertex count (*not* index count) or has none. All attributes are
+expected to not have an implementation-specific format.
+@see @ref isMeshIndexTypeImplementationSpecific(),
+    @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 1b53ebe00..e85d5875f 100644
--- a/src/Magnum/MeshTools/Test/DuplicateTest.cpp
+++ b/src/Magnum/MeshTools/Test/DuplicateTest.cpp
@@ -59,6 +59,7 @@ struct DuplicateTest: TestSuite::Tester {
 
     template<class T> void duplicateMeshData();
     void duplicateMeshDataNotIndexed();
+    void duplicateMeshDataImplementationSpecificIndexType();
     void duplicateMeshDataImplementationSpecificVertexFormat();
     void duplicateMeshDataExtra();
     void duplicateMeshDataExtraEmpty();
@@ -94,6 +95,7 @@ DuplicateTest::DuplicateTest() {
               &DuplicateTest::duplicateMeshData<UnsignedShort>,
               &DuplicateTest::duplicateMeshData<UnsignedInt>,
               &DuplicateTest::duplicateMeshDataNotIndexed,
+              &DuplicateTest::duplicateMeshDataImplementationSpecificIndexType,
               &DuplicateTest::duplicateMeshDataImplementationSpecificVertexFormat,
               &DuplicateTest::duplicateMeshDataExtra,
               &DuplicateTest::duplicateMeshDataExtraEmpty,
@@ -330,6 +332,24 @@ void DuplicateTest::duplicateMeshDataNotIndexed() {
     CORRADE_COMPARE(out.str(), "MeshTools::duplicate(): mesh data not indexed\n");
 }
 
+void DuplicateTest::duplicateMeshDataImplementationSpecificIndexType() {
+    #ifdef CORRADE_NO_ASSERT
+    CORRADE_SKIP("CORRADE_NO_ASSERT defined, can't test assertions");
+    #endif
+
+    Trade::MeshData a{MeshPrimitive::Lines,
+        nullptr, Trade::MeshIndexData{meshIndexTypeWrap(0xcaca), Containers::StridedArrayView1D<const void>{}},
+        nullptr, {
+        Trade::MeshAttributeData{Trade::MeshAttribute::Position,
+            VertexFormat::Vector3, nullptr},
+    }};
+
+    std::ostringstream out;
+    Error redirectError{&out};
+    MeshTools::duplicate(a);
+    CORRADE_COMPARE(out.str(), "MeshTools::duplicate(): mesh has an implementation-specific index type 0xcaca\n");
+}
+
 void DuplicateTest::duplicateMeshDataImplementationSpecificVertexFormat() {
     #ifdef CORRADE_NO_ASSERT
     CORRADE_SKIP("CORRADE_NO_ASSERT defined, can't test assertions");