diff --git a/include/box2d/types.h b/include/box2d/types.h
index e5d3b5fe..e653c716 100644
--- a/include/box2d/types.h
+++ b/include/box2d/types.h
@@ -156,32 +156,39 @@ typedef struct b2WorldDef
 	/// Stack allocator capacity. This controls how much space box2d reserves for per-frame calculations.
 	/// Larger worlds require more space. b2Counters can be used to determine a good capacity for your
 	/// application.
-	int32_t stackAllocatorCapacity;
+	int32_t arenaAllocatorCapacity;
 
 	/// task system hookup
 	uint32_t workerCount;
+
+	/// function to spawn task
 	b2EnqueueTaskCallback* enqueueTask;
+
+	/// function to finish a task
 	b2FinishTaskCallback* finishTask;
+
+	/// User context that is provided to enqueueTask and finishTask
 	void* userTaskContext;
 } b2WorldDef;
 
 /// Use this to initialize your world definition
-static inline b2WorldDef b2DefaultWorldDef(void)
-{
-	b2WorldDef def = B2_ZERO_INIT;
-	def.gravity = B2_LITERAL(b2Vec2){0.0f, -10.0f};
-	def.restitutionThreshold = 1.0f * b2_lengthUnitsPerMeter;
-	def.contactPushoutVelocity = 3.0f * b2_lengthUnitsPerMeter;
-	def.contactHertz = 30.0f;
-	def.contactDampingRatio = 1.0f;
-	def.enableSleep = true;
-	def.bodyCapacity = 8;
-	def.shapeCapacity = 8;
-	def.contactCapacity = 8;
-	def.jointCapacity = 8;
-	def.stackAllocatorCapacity = 1024 * 1024;
-	return def;
-}
+static const b2WorldDef b2_defaultWorldDef = {
+	{0.0f, -10.0f},				   // gravity
+	1.0f * b2_lengthUnitsPerMeter, // restitutionThreshold
+	3.0f * b2_lengthUnitsPerMeter, // contactPushoutVelocity
+	30.0,						   // contactHertz
+	1.0f,						   // contactDampingRatio
+	true,						   // enableSleep
+	0,							   // bodyCapacity
+	0,							   // shapeCapacity
+	0,							   // contactCapacity
+	0,							   // jointCapacity
+	1024 * 1024,				   // arenaAllocatorCapacity
+	0,							   // workerCount
+	NULL,						   // enqueueTask
+	NULL,						   // finishTask
+	NULL,						   // userTaskContext
+};
 
 /// The body type.
 /// static: zero mass, zero velocity, may be manually moved
@@ -248,7 +255,19 @@ typedef struct b2BodyDef
 
 /// Use this to initialize your body definition
 static const b2BodyDef b2_defaultBodyDef = {
-	b2_staticBody, {0.0f, 0.0f}, 0.0f, {0.0f, 0.0f}, 0.0f, 0.0f, 0.0f, 1.0f, NULL, true, true, false, true,
+	b2_staticBody, // bodyType
+	{0.0f, 0.0f},  // position
+	0.0f,		   // angle
+	{0.0f, 0.0f},  // linearVelocity
+	0.0f,		   // angularVelocity
+	0.0f,		   // linearDamping
+	0.0f,		   // angularDamping
+	1.0f,		   // gravityScale
+	NULL,		   // userData
+	true,		   // enableSleep
+	true,		   // isAwake
+	false,		   // fixedRotation
+	true,		   // isEnabled
 };
 
 /// This holds contact filtering data.
@@ -330,7 +349,15 @@ typedef struct b2ShapeDef
 
 /// Use this to initialize your shape definition
 static const b2ShapeDef b2_defaultShapeDef = {
-	NULL, 0.6f, 0.0f, 1.0f, {0x00000001, 0xFFFFFFFF, 0}, false, true, true, false,
+	NULL,						 // userData
+	0.6f,						 // friction
+	0.0f,						 // restitution
+	1.0f,						 // density
+	{0x00000001, 0xFFFFFFFF, 0}, // filter
+	false,						 // isSensor
+	true,						 // enableSensorEvents
+	true,						 // enableContactEvents
+	false,						 // enablePreSolveEvents
 };
 
 /// Used to create a chain of edges. This is designed to eliminate ghost collisions with some limitations.
@@ -370,7 +397,15 @@ typedef struct b2ChainDef
 } b2ChainDef;
 
 /// Use this to initialize your chain definition
-static const b2ChainDef b2_defaultChainDef = {NULL, 0, false, NULL, 0.6f, 0.0f, {0x00000001, 0xFFFFFFFF, 0}};
+static const b2ChainDef b2_defaultChainDef = {
+	NULL,						// points
+	0,							// count
+	false,						// loop
+	NULL,						// userData
+	0.6f,						// friction
+	0.0f,						// restitution
+	{0x00000001, 0xFFFFFFFF, 0} // filter
+};
 
 /// Profiling data. Times are in milliseconds.
 typedef struct b2Profile
diff --git a/samples/sample.cpp b/samples/sample.cpp
index a2060ec7..772e4fd2 100644
--- a/samples/sample.cpp
+++ b/samples/sample.cpp
@@ -56,7 +56,7 @@ Sample::Sample(const Settings& settings)
 	m_scheduler.Initialize(settings.workerCount);
 	m_taskCount = 0;
 
-	b2WorldDef worldDef = b2DefaultWorldDef();
+	b2WorldDef worldDef = b2_defaultWorldDef;
 	worldDef.workerCount = settings.workerCount;
 	worldDef.enqueueTask = &EnqueueTask;
 	worldDef.finishTask = &FinishTask;
@@ -66,7 +66,7 @@ Sample::Sample(const Settings& settings)
 	// These are not ideal, but useful for testing Box2D
 	worldDef.bodyCapacity = 2;
 	worldDef.contactCapacity = 2;
-	worldDef.stackAllocatorCapacity = 0;
+	worldDef.arenaAllocatorCapacity = 0;
 
 	m_worldId = b2CreateWorld(&worldDef);
 	m_textLine = 30;
diff --git a/src/world.c b/src/world.c
index e8c97032..7f6b411c 100644
--- a/src/world.c
+++ b/src/world.c
@@ -93,7 +93,7 @@ b2WorldId b2CreateWorld(const b2WorldDef* def)
 	world->index = id.index;
 
 	world->blockAllocator = b2CreateBlockAllocator();
-	world->stackAllocator = b2CreateStackAllocator(def->stackAllocatorCapacity);
+	world->stackAllocator = b2CreateStackAllocator(def->arenaAllocatorCapacity);
 
 	b2CreateBroadPhase(&world->broadPhase);
 	b2CreateGraph(&world->graph, def->bodyCapacity, def->contactCapacity, def->jointCapacity);
diff --git a/test/test_determinism.c b/test/test_determinism.c
index 731e2f11..e3807750 100644
--- a/test/test_determinism.c
+++ b/test/test_determinism.c
@@ -101,7 +101,7 @@ void TiltedStacks(int testIndex, int workerCount)
 	b2Vec2 gravity = {0.0f, -10.0f};
 
 	// Construct a world object, which will hold and simulate the rigid bodies.
-	b2WorldDef worldDef = b2DefaultWorldDef();
+	b2WorldDef worldDef = b2_defaultWorldDef;
 	worldDef.gravity = gravity;
 	worldDef.enqueueTask = EnqueueTask;
 	worldDef.finishTask = FinishTask;
diff --git a/test/test_world.c b/test/test_world.c
index 99ca0b9f..a2b48a4a 100644
--- a/test/test_world.c
+++ b/test/test_world.c
@@ -19,7 +19,7 @@ int HelloWorld(void)
 	b2Vec2 gravity = {0.0f, -10.0f};
 
 	// Construct a world object, which will hold and simulate the rigid bodies.
-	b2WorldDef worldDef = b2DefaultWorldDef();
+	b2WorldDef worldDef = b2_defaultWorldDef;
 	worldDef.gravity = gravity;
 
 	b2WorldId worldId = b2CreateWorld(&worldDef);
@@ -98,7 +98,7 @@ int HelloWorld(void)
 
 int EmptyWorld(void)
 {
-	b2WorldDef worldDef = b2DefaultWorldDef();
+	b2WorldDef worldDef = b2_defaultWorldDef;
 	b2WorldId worldId = b2CreateWorld(&worldDef);
 	ENSURE(b2World_IsValid(worldId) == true);