diff --git a/src/Magnum/MeshTools/Interleave.cpp b/src/Magnum/MeshTools/Interleave.cpp
index 778802ccf..219fc71c1 100644
--- a/src/Magnum/MeshTools/Interleave.cpp
+++ b/src/Magnum/MeshTools/Interleave.cpp
@@ -265,11 +265,10 @@ Trade::MeshData interleave(Trade::MeshData&& data, const Containers::ArrayView<c
     Trade::MeshIndexData indices;
     if(data.isIndexed()) {
         const MeshIndexType indexType = data.indexType();
-        const std::size_t indexTypeSize = meshIndexTypeSize(indexType);
 
         /* If we can steal the data and we're allowed to preserve a strided
            layout or it's tightly packed, do the steal */
-        if((data.indexDataFlags() & Trade::DataFlag::Owned) && ((flags & InterleaveFlag::PreserveStridedIndices) || data.indexStride() == Int(indexTypeSize))) {
+        if((data.indexDataFlags() & Trade::DataFlag::Owned) && ((flags & InterleaveFlag::PreserveStridedIndices) || (!isMeshIndexTypeImplementationSpecific(indexType) && data.indexStride() == Int(meshIndexTypeSize(indexType))))) {
             indices = Trade::MeshIndexData{indexType,
                 Containers::StridedArrayView1D<const void>{
                     data.indexData(),
@@ -291,8 +290,14 @@ Trade::MeshData interleave(Trade::MeshData&& data, const Containers::ArrayView<c
                     data.indexStride()}};
             Utility::copy(data.indexData(), indexData);
 
-        /* Otherwise, make a tightly packed copy */
+        /* Otherwise, make a tightly packed copy, in which case we can't have
+           an implementation-specific index type */
         } else {
+            CORRADE_ASSERT(!isMeshIndexTypeImplementationSpecific(indexType),
+                "MeshTools::interleave(): mesh has an implementation-specific index type" << reinterpret_cast<void*>(meshIndexTypeUnwrap(indexType)) << Debug::nospace << ", enable MeshTools::InterleaveFlag::PreserveStridedIndices to pass the array through unchanged",
+                (Trade::MeshData{MeshPrimitive{}, 0}));
+
+            const std::size_t indexTypeSize = meshIndexTypeSize(indexType);
             indexData = Containers::Array<char>{NoInit, data.indexCount()*indexTypeSize};
             Containers::StridedArrayView2D<char> out{indexData,
                 {data.indexCount(), indexTypeSize},
diff --git a/src/Magnum/MeshTools/Interleave.h b/src/Magnum/MeshTools/Interleave.h
index 4420aabc1..ece30f231 100644
--- a/src/Magnum/MeshTools/Interleave.h
+++ b/src/Magnum/MeshTools/Interleave.h
@@ -219,12 +219,14 @@ enum class InterleaveFlag: UnsignedInt {
      *
      * If not set and the index buffer is strided, a tightly packed copy with
      * the same index type is allocated for the output, dropping also any
-     * padding before or after the original index view.
+     * padding before or after the original index view. In such case however,
+     * the index type is not allowed to be implementation-specific.
      *
      * Has no effect when passed to @ref interleavedLayout(const Trade::MeshData&, UnsignedInt, Containers::ArrayView<const Trade::MeshAttributeData>, InterleaveFlags) "interleavedLayout()"
      * as that function doesn't preserve the index buffer. Has no effect when
      * passed to @ref concatenate(Containers::ArrayView<const Containers::Reference<const Trade::MeshData>>, InterleaveFlags) "concatenate()"
      * as that function allocates a new combined index buffer anyway.
+     * @see @ref isMeshIndexTypeImplementationSpecific()
      */
     PreserveStridedIndices = 1 << 1
 };
@@ -361,8 +363,9 @@ it, see its documentation for detailed behavior description. Note that
 offset-only @ref Trade::MeshAttributeData instances are not supported in the
 @p extra array.
 
-Indices (if any) are kept as-is only if they're tightly packed. Otherwise the
-behavior depends on presence of @ref InterleaveFlag::PreserveStridedIndices.
+Indices (if any) are kept as-is only if they're tightly packed and not with an
+implementation-specific type. Otherwise the behavior depends on presence of
+@ref InterleaveFlag::PreserveStridedIndices.
 
 Expects that each attribute in @p extra has either the same amount of elements
 as @p data vertex count or has none. This function will unconditionally make a
@@ -373,7 +376,8 @@ to avoid that copy.
 All attributes in both @p data and @p extra are expected to not have an
 implementation-specific format, except for @p data attributes in case @p data
 is already interleaved, then the layout is untouched.
-@see @ref isInterleaved(), @ref isVertexFormatImplementationSpecific(),
+@see @ref isInterleaved(), @ref isMeshIndexTypeImplementationSpecific(),
+    @ref isVertexFormatImplementationSpecific(),
     @ref Trade::MeshData::attributeData()
 */
 MAGNUM_MESHTOOLS_EXPORT Trade::MeshData interleave(const Trade::MeshData& data, Containers::ArrayView<const Trade::MeshAttributeData> extra = {}, InterleaveFlags flags = InterleaveFlag::PreserveInterleavedAttributes);
diff --git a/src/Magnum/MeshTools/Test/InterleaveTest.cpp b/src/Magnum/MeshTools/Test/InterleaveTest.cpp
index 834b54917..9308fd6ad 100644
--- a/src/Magnum/MeshTools/Test/InterleaveTest.cpp
+++ b/src/Magnum/MeshTools/Test/InterleaveTest.cpp
@@ -86,6 +86,7 @@ struct InterleaveTest: Corrade::TestSuite::Tester {
 
     void interleaveMeshData();
     void interleaveMeshDataIndexed();
+    void interleaveMeshDataImplementationSpecificIndexType();
     void interleaveMeshDataImplementationSpecificVertexFormat();
     void interleaveMeshDataExtra();
     void interleaveMeshDataExtraEmpty();
@@ -112,13 +113,15 @@ const struct {
 
 const struct {
     const char* name;
+    MeshIndexType indexType;
     Containers::Optional<InterleaveFlags> flags;
     bool flip;
     bool shouldPreserveLayoutInCopy, shouldPreserveLayoutInMove;
 } StridedIndicesData[]{
-    {"", {}, false, false, true},
-    {"strided indices", {}, true, false, false},
-    {"strided indices, preserved", InterleaveFlag::PreserveInterleavedAttributes|InterleaveFlag::PreserveStridedIndices, true, true, true}
+    {"", MeshIndexType::UnsignedShort, {}, false, false, true},
+    {"strided indices", MeshIndexType::UnsignedShort, {}, true, false, false},
+    {"strided indices, preserved", MeshIndexType::UnsignedShort, InterleaveFlag::PreserveInterleavedAttributes|InterleaveFlag::PreserveStridedIndices, true, true, true},
+    {"strided indices, implementation-specific index type, preserved", meshIndexTypeWrap(0xbaf), InterleaveFlag::PreserveInterleavedAttributes|InterleaveFlag::PreserveStridedIndices, true, true, true}
 };
 
 InterleaveTest::InterleaveTest() {
@@ -171,7 +174,8 @@ InterleaveTest::InterleaveTest() {
     addInstancedTests({&InterleaveTest::interleaveMeshDataIndexed},
         Containers::arraySize(StridedIndicesData));
 
-    addTests({&InterleaveTest::interleaveMeshDataImplementationSpecificVertexFormat,
+    addTests({&InterleaveTest::interleaveMeshDataImplementationSpecificIndexType,
+              &InterleaveTest::interleaveMeshDataImplementationSpecificVertexFormat,
               &InterleaveTest::interleaveMeshDataExtra,
               &InterleaveTest::interleaveMeshDataExtraEmpty,
               &InterleaveTest::interleaveMeshDataExtraOriginalEmpty,
@@ -1192,7 +1196,7 @@ void InterleaveTest::interleaveMeshDataIndexed() {
 
     Vector2 positions[]{{1.3f, 0.3f}, {0.87f, 1.1f}, {1.0f, -0.5f}};
     Trade::MeshData mesh{MeshPrimitive::TriangleFan,
-        {}, Containers::arrayView(indexData), Trade::MeshIndexData{indices},
+        {}, Containers::arrayView(indexData), Trade::MeshIndexData{data.indexType, indices},
         {}, Containers::arrayView(positions), {
             Trade::MeshAttributeData{Trade::MeshAttribute::Position, Containers::arrayView(positions)}
         }};
@@ -1204,8 +1208,8 @@ void InterleaveTest::interleaveMeshDataIndexed() {
     CORRADE_COMPARE(interleaved.primitive(), MeshPrimitive::TriangleFan);
 
     CORRADE_VERIFY(interleaved.isIndexed());
-    CORRADE_COMPARE(interleaved.indexType(), MeshIndexType::UnsignedShort);
-    CORRADE_COMPARE_AS(interleaved.indices<UnsignedShort>(),
+    CORRADE_COMPARE(interleaved.indexType(), data.indexType);
+    CORRADE_COMPARE_AS((Containers::arrayCast<1, const UnsignedShort>(interleaved.indices())),
         Containers::arrayView<UnsignedShort>({0, 2, 1}),
         TestSuite::Compare::Container);
 
@@ -1227,6 +1231,23 @@ void InterleaveTest::interleaveMeshDataIndexed() {
         TestSuite::Compare::Container);
 }
 
+void InterleaveTest::interleaveMeshDataImplementationSpecificIndexType() {
+    #ifdef CORRADE_NO_ASSERT
+    CORRADE_SKIP("CORRADE_NO_ASSERT defined, can't test assertions");
+    #endif
+
+    Trade::MeshData data{MeshPrimitive::Points,
+        nullptr, Trade::MeshIndexData{meshIndexTypeWrap(0xcaca), Containers::StridedArrayView1D<const void>{}},
+        nullptr, {
+            Trade::MeshAttributeData{Trade::MeshAttribute::Position, VertexFormat::Vector2, nullptr}
+        }};
+
+    std::ostringstream out;
+    Error redirectError{&out};
+    MeshTools::interleave(data);
+    CORRADE_COMPARE(out.str(), "MeshTools::interleave(): mesh has an implementation-specific index type 0xcaca, enable MeshTools::InterleaveFlag::PreserveStridedIndices to pass the array through unchanged\n");
+}
+
 void InterleaveTest::interleaveMeshDataImplementationSpecificVertexFormat() {
     #ifdef CORRADE_NO_ASSERT
     CORRADE_SKIP("CORRADE_NO_ASSERT defined, can't test assertions");
@@ -1438,7 +1459,7 @@ void InterleaveTest::interleaveMeshDataAlreadyInterleavedMoveIndices() {
     const Trade::MeshAttributeData* attributePointer = attributeData;
 
     Trade::MeshData mesh{MeshPrimitive::TriangleFan,
-        std::move(indexData), Trade::MeshIndexData{indices},
+        std::move(indexData), Trade::MeshIndexData{data.indexType,indices},
         std::move(vertexData), std::move(attributeData)};
     CORRADE_VERIFY(MeshTools::isInterleaved(mesh));
 
@@ -1448,8 +1469,8 @@ void InterleaveTest::interleaveMeshDataAlreadyInterleavedMoveIndices() {
         MeshTools::interleave(std::move(mesh));
 
     CORRADE_VERIFY(MeshTools::isInterleaved(interleaved));
-    CORRADE_COMPARE(interleaved.indexType(), MeshIndexType::UnsignedShort);
-    CORRADE_COMPARE_AS(interleaved.indices<UnsignedShort>(),
+    CORRADE_COMPARE(interleaved.indexType(), data.indexType);
+    CORRADE_COMPARE_AS((Containers::arrayCast<1, const UnsignedShort>(interleaved.indices())),
         Containers::arrayView<UnsignedShort>({0, 2, 1}),
         TestSuite::Compare::Container);