diff --git a/src/Magnum/Math/Frustum.h b/src/Magnum/Math/Frustum.h
index cd300b5d6..9ac7c020c 100644
--- a/src/Magnum/Math/Frustum.h
+++ b/src/Magnum/Math/Frustum.h
@@ -122,9 +122,15 @@ template<class T> class Frustum {
             return Corrade::Containers::StaticArrayView<6, const Vector4<T>>{_data};
         }
 
-        /** @brief Plane at given index */
+        /**
+         * @brief Plane at given index
+         *
+         * Expects that @p i is less than @cpp 6 @ce.
+         */
         /* returns const& so [][] operations are also constexpr */
-        constexpr const Vector4<T>& operator[](std::size_t i) const { return _data[i]; }
+        constexpr const Vector4<T>& operator[](std::size_t i) const {
+            return CORRADE_CONSTEXPR_ASSERT(i < 6, "Math::Frustum::operator[](): index" << i << "out of range"), _data[i];
+        }
 
         /** @brief Left plane */
         constexpr Vector4<T> left() const { return _data[0]; }
diff --git a/src/Magnum/Math/Test/CMakeLists.txt b/src/Magnum/Math/Test/CMakeLists.txt
index c65a57440..459935561 100644
--- a/src/Magnum/Math/Test/CMakeLists.txt
+++ b/src/Magnum/Math/Test/CMakeLists.txt
@@ -75,6 +75,7 @@ set_property(TARGET
     MathComplexTest
     MathCubicHermiteTest
     MathDualComplexTest
+    MathFrustumTest
     MathQuaternionTest
     MathDualQuaternionTest
 
diff --git a/src/Magnum/Math/Test/FrustumTest.cpp b/src/Magnum/Math/Test/FrustumTest.cpp
index 9fc2b7ac8..0bfde3772 100644
--- a/src/Magnum/Math/Test/FrustumTest.cpp
+++ b/src/Magnum/Math/Test/FrustumTest.cpp
@@ -283,6 +283,11 @@ void FrustumTest::data() {
     #endif
     Float b = *a.data();
     CORRADE_COMPARE(b, 1.0f);
+
+    std::ostringstream out;
+    Error redirectError{&out};
+    a[6];
+    CORRADE_COMPARE(out.str(), "Math::Frustum::operator[](): index 6 out of range\n");
 }
 
 void FrustumTest::compare() {