diff --git a/src/libcalamares/CMakeLists.txt b/src/libcalamares/CMakeLists.txt
index 87338ae6c..f942dbde1 100644
--- a/src/libcalamares/CMakeLists.txt
+++ b/src/libcalamares/CMakeLists.txt
@@ -207,6 +207,16 @@ if ( ECM_FOUND AND BUILD_TESTING )
             Qt5::Test
     )
     calamares_automoc( libcalamaresnetworktest )
+
+    ecm_add_test(
+            modulesystem/Tests.cpp
+        TEST_NAME
+            libcalamaresmodulesystemtest
+        LINK_LIBRARIES
+            calamares
+            Qt5::Test
+    )
+    calamares_automoc( libcalamaresmodulesystemtest )
 endif()
 
 if( BUILD_TESTING )
diff --git a/src/libcalamares/modulesystem/InstanceKey.h b/src/libcalamares/modulesystem/InstanceKey.h
index 8e04dbaef..80be23941 100644
--- a/src/libcalamares/modulesystem/InstanceKey.h
+++ b/src/libcalamares/modulesystem/InstanceKey.h
@@ -52,12 +52,14 @@ public:
         {
             second = first;
         }
+        validate();
     }
 
     /// @brief Create "usual" instances keys `module@module`
     explicit InstanceKey( const QString& module )
         : QPair( module, module )
     {
+        validate();
     }
 
     /// @brief Create unusual, invalid instance key
@@ -89,6 +91,16 @@ public:
         return InstanceKey( moduleEntrySplit.first(), moduleEntrySplit.last() );
     }
 
+private:
+    /** @brief Check validity and reset module and id if needed. */
+    void validate()
+    {
+        if ( first.contains( '@' ) || second.contains( '@' ) )
+        {
+            first = QString();
+            second = QString();
+        }
+    }
 };
 
 }
diff --git a/src/libcalamares/modulesystem/Tests.cpp b/src/libcalamares/modulesystem/Tests.cpp
new file mode 100644
index 000000000..b54d020c5
--- /dev/null
+++ b/src/libcalamares/modulesystem/Tests.cpp
@@ -0,0 +1,129 @@
+/* === This file is part of Calamares - <https://github.com/calamares> ===
+ *
+ *   Copyright 2019, Adriaan de Groot <groot@kde.org>
+ *
+ *   Calamares is free software: you can redistribute it and/or modify
+ *   it under the terms of the GNU General Public License as published by
+ *   the Free Software Foundation, either version 3 of the License, or
+ *   (at your option) any later version.
+ *
+ *   Calamares is distributed in the hope that it will be useful,
+ *   but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ *   GNU General Public License for more details.
+ *
+ *   You should have received a copy of the GNU General Public License
+ *   along with Calamares. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include "modulesystem/InstanceKey.h"
+
+#include <QtTest/QtTest>
+
+using Calamares::ModuleSystem::InstanceKey;
+
+class ModuleSystemTests : public QObject
+{
+    Q_OBJECT
+public:
+    ModuleSystemTests() {}
+    virtual ~ModuleSystemTests() {}
+
+private Q_SLOTS:
+    void initTestCase();
+
+    void testEmptyInstanceKey();
+    void testSimpleInstanceKey();
+    void testCustomInstanceKey();
+    void testFromStringInstanceKey();
+
+    void testBadSimpleCases();
+    void testBadFromStringCases();
+};
+
+void ModuleSystemTests::initTestCase()
+{
+}
+
+void assert_is_invalid( const InstanceKey& k )
+{
+    QVERIFY( !k.isValid() );
+    QVERIFY( !k.isCustom() );
+    QVERIFY( k.module().isEmpty() );
+    QVERIFY( k.id().isEmpty() );
+}
+
+void ModuleSystemTests::testEmptyInstanceKey()
+{
+    InstanceKey k0;
+    assert_is_invalid( k0 );
+}
+
+void ModuleSystemTests::testSimpleInstanceKey()
+{
+    InstanceKey k1( "derp" );
+    QVERIFY( k1.isValid() );
+    QVERIFY( !k1.isCustom() );
+    QCOMPARE( k1.module(), QStringLiteral( "derp" ) );
+    QCOMPARE( k1.id(), QStringLiteral( "derp" ) );
+}
+
+void ModuleSystemTests::testCustomInstanceKey()
+{
+    InstanceKey k0("derp", "derp");
+    QVERIFY( k0.isValid() );
+    QVERIFY( !k0.isCustom() );
+    QCOMPARE( k0.module(), QStringLiteral( "derp" ) );
+    QCOMPARE( k0.id(), QStringLiteral( "derp" ) );
+
+    InstanceKey k1("derp", "horse");
+    QVERIFY( k1.isValid() );
+    QVERIFY( k1.isCustom() );
+    QCOMPARE( k1.module(), QStringLiteral( "derp" ) );
+    QCOMPARE( k1.id(), QStringLiteral( "horse" ) );
+}
+
+void ModuleSystemTests::testFromStringInstanceKey()
+{
+    InstanceKey k0 = InstanceKey::fromString( "derp@derp" );
+    QVERIFY( k0.isValid() );
+    QVERIFY( !k0.isCustom() );
+    QCOMPARE( k0.module(), QStringLiteral( "derp" ) );
+    QCOMPARE( k0.id(), QStringLiteral( "derp" ) );
+
+    InstanceKey k1 = InstanceKey::fromString( "derp@horse" );
+    QVERIFY( k1.isValid() );
+    QVERIFY( k1.isCustom() );
+    QCOMPARE( k1.module(), QStringLiteral( "derp" ) );
+    QCOMPARE( k1.id(), QStringLiteral( "horse" ) );
+
+    InstanceKey k2 = InstanceKey::fromString( "derp" );
+    QVERIFY( k2.isValid() );
+    QVERIFY( !k2.isCustom() );
+    QCOMPARE( k2.module(), QStringLiteral( "derp" ) );
+    QCOMPARE( k2.id(), QStringLiteral( "derp" ) );
+}
+
+/// @brief These are expected to fail since they show bugs in the code
+void ModuleSystemTests::testBadSimpleCases()
+{
+    InstanceKey k2( "derp@derp" );
+    assert_is_invalid( k2 );
+
+    InstanceKey k3( "derp@horse" );
+    assert_is_invalid( k3 );
+}
+
+void ModuleSystemTests::testBadFromStringCases()
+{
+    InstanceKey k0 = InstanceKey::fromString( QString() );
+    assert_is_invalid( k0 );
+
+    k0 = InstanceKey::fromString( "derp@derp@derp" );
+    assert_is_invalid( k0 );
+}
+
+
+QTEST_GUILESS_MAIN( ModuleSystemTests )
+
+#include "Tests.moc"