diff --git a/repos/libports/src/test/spark/machinery.adb b/repos/libports/src/test/spark/machinery.adb
index 23a3e4795f..47e835ed2c 100644
--- a/repos/libports/src/test/spark/machinery.adb
+++ b/repos/libports/src/test/spark/machinery.adb
@@ -2,6 +2,11 @@ pragma Ada_2012;
 
 package body Machinery is
 
+   function Number_Of_Bits (Machinery : Machinery_Type) return Number_Of_Bits_Type is
+   begin
+      return Machinery'Size;
+   end Number_Of_Bits;
+
    procedure Initialize (Machinery : out Machinery_Type) is
    begin
       Machinery := ( Temperature => 25 );
diff --git a/repos/libports/src/test/spark/machinery.ads b/repos/libports/src/test/spark/machinery.ads
index 947ed05397..db446d06fc 100644
--- a/repos/libports/src/test/spark/machinery.ads
+++ b/repos/libports/src/test/spark/machinery.ads
@@ -2,10 +2,17 @@ package Machinery is
 
    pragma Pure;
 
+   type Number_Of_Bits_Type is mod 2**32 with Size => 32;
+
    type Temperature_Type is mod 2**32 with Size => 32;
 
    type Machinery_Type is private;
 
+   function Number_of_bits (Machinery : Machinery_Type) return Number_Of_Bits_Type
+     with Export,
+          Convention    => C,
+          External_Name => "_ZN5Spark14number_of_bitsERKNS_9MachineryE";
+
    procedure Initialize (Machinery : out Machinery_Type)
      with Export,
           Convention    => C,
diff --git a/repos/libports/src/test/spark/machinery.h b/repos/libports/src/test/spark/machinery.h
index b1c79dcc15..dd1cfdf662 100644
--- a/repos/libports/src/test/spark/machinery.h
+++ b/repos/libports/src/test/spark/machinery.h
@@ -20,6 +20,13 @@ namespace Spark {
 	template <Genode::size_t BYTES>
 	struct Object
 	{
+		/**
+		 * Exception type
+		 */
+		struct Object_size_mismatch { };
+
+		static constexpr Genode::size_t bytes() { return BYTES; }
+
 		long _space[(BYTES + sizeof(long) - 1)/sizeof(long)] { };
 	};
 
@@ -31,6 +38,15 @@ namespace Spark {
 
 		Genode::uint32_t temperature() const;
 	};
+
+	Genode::size_t number_of_bits(Machinery const &);
+
+	template <typename T>
+	static inline void assert_valid_object_size()
+	{
+		if (number_of_bits(*(T *)nullptr) > T::bytes()*8)
+			throw typename T::Object_size_mismatch();
+	}
 }
 
 
@@ -38,6 +54,8 @@ static inline void test_spark_object_construction()
 {
 	using namespace Genode;
 
+	Spark::assert_valid_object_size<Spark::Machinery>();
+
 	Spark::Machinery machinery { };
 
 	auto check = [&] (char const *msg, Genode::uint32_t expected)