diff --git a/Library/include/playrho/Contact.hpp b/Library/include/playrho/Contact.hpp
index a8691aa9d1..bffc6d1cee 100644
--- a/Library/include/playrho/Contact.hpp
+++ b/Library/include/playrho/Contact.hpp
@@ -67,6 +67,9 @@ struct ToiConf;
 class Contact
 {
 public:
+    /// @brief Default contactable value.
+    static constexpr auto DefaultContactable = Contactable{InvalidBodyID, InvalidShapeID, 0};
+
     /// @brief Substep type.
     using substep_type = TimestepIters;
 
@@ -74,7 +77,11 @@ class Contact
     constexpr Contact() noexcept = default;
 
     /// @brief Initializing constructor.
-    /// @note This need never be called directly by a user.
+    /// @param a The "a" contactable value.
+    /// @param b The "b" contactable value.
+    /// @post If either @p a or @p b is not the value of @c DefaultContactable then:
+    ///   <code>IsEnabled()</code> and <code>NeedsUpdating()</code> return true,
+    ///   else they return false.
     constexpr Contact(const Contactable& a, const Contactable& b) noexcept;
 
     /// @brief Is this contact touching?
@@ -290,10 +297,10 @@ class Contact
     };
 
     /// @brief Identifying info for the A-side of the 2-bodied contact.
-    Contactable m_contactableA{InvalidBodyID, InvalidShapeID, 0};
+    Contactable m_contactableA = DefaultContactable;
 
     /// @brief Identifying info for the B-side of the 2-bodied contact.
-    Contactable m_contactableB{InvalidBodyID, InvalidShapeID, 0};
+    Contactable m_contactableB = DefaultContactable;
 
     // initialized on construction (construction-time depedent)
 
@@ -322,7 +329,8 @@ class Contact
 constexpr Contact::Contact(const Contactable& a, const Contactable& b) noexcept
     : m_contactableA{a},
       m_contactableB{b},
-      m_flags{e_enabledFlag | e_dirtyFlag}
+      m_flags{((a != DefaultContactable) || (b != DefaultContactable))
+          ? FlagsType(e_enabledFlag | e_dirtyFlag): FlagsType{}}
 {
 }
 
@@ -516,7 +524,8 @@ constexpr void Contact::IncrementToiCount() noexcept
 /// @relatedalso Contact
 constexpr bool operator==(const Contact& lhs, const Contact& rhs) noexcept
 {
-    return lhs.GetContactableA() == rhs.GetContactableB() && //
+    return lhs.GetContactableA() == rhs.GetContactableA() && //
+           lhs.GetContactableB() == rhs.GetContactableB() && //
            lhs.GetFriction() == rhs.GetFriction() && //
            lhs.GetRestitution() == rhs.GetRestitution() && //
            lhs.GetTangentSpeed() == rhs.GetTangentSpeed() && //
diff --git a/UnitTests/Contact.cpp b/UnitTests/Contact.cpp
index 666604e293..703be650c1 100644
--- a/UnitTests/Contact.cpp
+++ b/UnitTests/Contact.cpp
@@ -25,29 +25,6 @@
 using namespace playrho;
 using namespace playrho::d2;
 
-TEST(Contact, ByteSize)
-{
-    // Check size at test runtime instead of compile-time via static_assert to avoid stopping
-    // builds and to report actual size rather than just reporting that expected size is wrong.
-    switch (sizeof(Real))
-    {
-        case  4:
-            EXPECT_EQ(alignof(Contact), 4u);
-            EXPECT_EQ(sizeof(Contact), std::size_t(36));
-            break;
-        case  8:
-            EXPECT_EQ(alignof(Contact), 8u);
-            EXPECT_EQ(sizeof(Contact), std::size_t(56));
-            break;
-        case 16:
-            EXPECT_EQ(sizeof(Contact), std::size_t(96));
-            break;
-        default:
-            FAIL();
-            break;
-    }
-}
-
 TEST(Contact, Enabled)
 {
     const auto bA = BodyID(0u);
@@ -63,6 +40,11 @@ TEST(Contact, Enabled)
 
 TEST(Contact, DefaultConstruction)
 {
+    {
+        const auto c = Contact();
+        EXPECT_EQ(c.GetContactableA(), Contact::DefaultContactable);
+        EXPECT_EQ(c.GetContactableB(), Contact::DefaultContactable);
+    }
     EXPECT_EQ(GetBodyA(Contact()), InvalidBodyID);
     EXPECT_EQ(GetBodyB(Contact()), InvalidBodyID);
     EXPECT_EQ(GetShapeA(Contact()), InvalidShapeID);
@@ -218,3 +200,78 @@ TEST(Contact, GetOtherBody)
     EXPECT_EQ(GetOtherBody(contact, bodyIdA), bodyIdB);
     EXPECT_EQ(GetOtherBody(contact, bodyIdB), bodyIdA);
 }
+
+TEST(Contact, Equality)
+{
+    EXPECT_TRUE(Contact() == Contact());
+    EXPECT_TRUE(Contact() == Contact(Contact::DefaultContactable, Contact::DefaultContactable));
+    {
+        auto c = Contact();
+        c.SetTouching();
+        EXPECT_FALSE(Contact() == c);
+    }
+    {
+        auto c = Contact();
+        c.SetEnabled();
+        EXPECT_FALSE(Contact() == c);
+    }
+    {
+        auto c = Contact();
+        c.SetFriction(NonNegative<Real>(2));
+        EXPECT_FALSE(Contact() == c);
+    }
+    {
+        auto c = Contact();
+        c.SetRestitution(Real(42));
+        EXPECT_FALSE(Contact() == c);
+    }
+    {
+        auto c = Contact();
+        c.SetTangentSpeed(42_mps);
+        EXPECT_FALSE(Contact() == c);
+    }
+    {
+        auto c = Contact();
+        c.SetToiCount(42u);
+        EXPECT_FALSE(Contact() == c);
+    }
+    {
+        auto c = Contact();
+        c.SetToi(std::optional<UnitIntervalFF<Real>>(0.5));
+        EXPECT_FALSE(Contact() == c);
+    }
+    {
+        auto c = Contact();
+        c.FlagForFiltering();
+        EXPECT_FALSE(Contact() == c);
+    }
+    {
+        auto c = Contact();
+        c.FlagForUpdating();
+        EXPECT_FALSE(Contact() == c);
+    }
+    {
+        auto c = Contact();
+        c.SetSensor();
+        EXPECT_FALSE(Contact() == c);
+    }
+    {
+        auto c = Contact();
+        c.SetImpenetrable();
+        EXPECT_FALSE(Contact() == c);
+    }
+    {
+        auto c = Contact();
+        c.SetIsActive();
+        EXPECT_FALSE(Contact() == c);
+    }
+    EXPECT_FALSE(Contact() ==
+                 Contact(Contactable{BodyID(1u), ShapeID(0u), ChildCounter(0u)},
+                         Contact::DefaultContactable));
+    EXPECT_FALSE(Contact() ==
+                 Contact(Contactable{BodyID(0u), ShapeID(1u), ChildCounter(0u)},
+                         Contact::DefaultContactable));
+    EXPECT_FALSE(Contact() ==
+                 Contact(Contactable{BodyID(0u), ShapeID(0u), ChildCounter(1u)},
+                         Contact::DefaultContactable));
+}