diff --git a/CHANGELOG.md b/CHANGELOG.md
index c08b867..6053c48 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -12,6 +12,10 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Add `CHANGELOG.md`
 - Add markdown linter to CI
 
+### Fixed
+
+- Fix passing `None` to `RegistersTracker.processLui`
+
 ## [1.7.9] - 2023-09-18
 
 ### Changed
diff --git a/docs/usage_c_api.md b/docs/usage_c_api.md
index 3cfcb03..33c2151 100644
--- a/docs/usage_c_api.md
+++ b/docs/usage_c_api.md
@@ -73,11 +73,11 @@ Let's break up the example and explain each part:
     To initialize our `instr` we need to call the pair `RabbitizerInstruction_init`
     and `RabbitizerInstruction_processUniqueId`. `RabbitizerInstruction_init`
     initialises all the members of the struct so it doesn't contain garbage data
-    anymore, while `RabbitizerInstruction_processUniqueId` does the heavy lifting of
-    identifying the actual instruction id out of the `word` we passed.
+    anymore, while `RabbitizerInstruction_processUniqueId` does the heavy lifting
+    of identifying the actual instruction id out of the `word` we passed.
 
-    A `RabbitizerInstruction` variable is not considered fully initialized until it
-    has been passed to this pair of functions.
+    A `RabbitizerInstruction` variable is not considered fully initialized until
+    it has been passed to this pair of functions.
 
     ```c
         RabbitizerInstruction_init(&instr, word, vram);
diff --git a/rabbitizer/rabbitizer_module.h b/rabbitizer/rabbitizer_module.h
index 2800ff5..d11b8bd 100644
--- a/rabbitizer/rabbitizer_module.h
+++ b/rabbitizer/rabbitizer_module.h
@@ -44,6 +44,11 @@ extern PyTypeObject rabbitizer_type_LoPairingInfo_TypeObject;
 extern PyTypeObject rabbitizer_type_TrackedRegisterState_TypeObject;
 extern PyTypeObject rabbitizer_type_RegistersTracker_TypeObject;
 
+int rabbitizer_type_Instruction_TypeObject_Check(PyObject *o);
+
+int rabbitizer_converter_InstructionOrNone(PyObject *object, PyRabbitizerInstruction **address);
+
+
 DECL_ENUM(Abi)
 DECL_ENUM(InstrCategory)
 DECL_ENUM(InstrId)
diff --git a/rabbitizer/rabbitizer_type_Instruction.c b/rabbitizer/rabbitizer_type_Instruction.c
index 967cc16..c324875 100644
--- a/rabbitizer/rabbitizer_type_Instruction.c
+++ b/rabbitizer/rabbitizer_type_Instruction.c
@@ -671,6 +671,57 @@ static PyObject *rabbitizer_type_Instruction_str(PyRabbitizerInstruction *self)
     return rabbitizer_type_Instruction_disassemble(self, Py_BuildValue("()"), Py_BuildValue("{}"));
 }
 
+/**
+ * Returns:
+ *  - 1 if `o` is an RabbitizerInstruction
+ *  - 0 if not an instance of RabbitizerInstruction
+ *  - -1 if an error occurred
+ */
+int rabbitizer_type_Instruction_TypeObject_Check(PyObject *o) {
+    int isInstance = PyObject_IsInstance(o, (PyObject*)&rabbitizer_type_Instruction_TypeObject);
+
+    if (isInstance < 0) {
+        /* An error happened */
+        /* PyObject_IsInstance already sets an exception, so nothing else to do here */
+        return -1;
+    }
+
+    if (isInstance == 0) {
+        /* `o` isn't an instance of RabbitizerInstruction */
+        return 0;
+    }
+
+    return 1;
+}
+
+
+int rabbitizer_converter_InstructionOrNone(PyObject *object, PyRabbitizerInstruction **address) {
+    int instanceCheck;
+
+    if ((object == NULL) || (address == NULL)) {
+        PyErr_Format(PyExc_RuntimeError, "%s: Internal error", __func__);
+        return 0; // fail
+    }
+
+    if (object == Py_None) {
+        *address = NULL;
+        return 1; // successful
+    }
+
+    instanceCheck = rabbitizer_type_Instruction_TypeObject_Check(object);
+    if (instanceCheck < 0) {
+        return 0; // fail
+    }
+    if (instanceCheck > 0) {
+        *address = (PyRabbitizerInstruction*)object;
+        return 1; // successful
+    }
+
+    // TypeError: argument 3 must be rabbitizer.Instruction, not None
+    PyErr_Format(PyExc_TypeError, "argument must be %s or None, not %s", rabbitizer_type_Instruction_TypeObject.tp_name, object->ob_type->tp_name);
+    return 0; // fail
+}
+
 
 PyTypeObject rabbitizer_type_Instruction_TypeObject = {
     PyVarObject_HEAD_INIT(NULL, 0)
diff --git a/rabbitizer/rabbitizer_type_RegistersTracker.c b/rabbitizer/rabbitizer_type_RegistersTracker.c
index 485ef05..539259e 100644
--- a/rabbitizer/rabbitizer_type_RegistersTracker.c
+++ b/rabbitizer/rabbitizer_type_RegistersTracker.c
@@ -11,7 +11,6 @@ typedef struct PyRabbitizerRegistersTracker {
     RabbitizerRegistersTracker tracker;
 } PyRabbitizerRegistersTracker;
 
-
 static void rabbitizer_type_RegistersTracker_dealloc(PyRabbitizerRegistersTracker *self) {
     RabbitizerRegistersTracker_destroy(&self->tracker);
     Py_TYPE(self)->tp_free((PyObject *) self);
@@ -119,7 +118,7 @@ static PyObject *rabbitizer_type_RegistersTracker_processLui(PyRabbitizerRegiste
     PyRabbitizerInstruction *pyPrevInstr = NULL;
     RabbitizerInstruction *prevInstr = NULL;
 
-    if (!PyArg_ParseTupleAndKeywords(args, kwds, "O!i|O!", kwlist, &rabbitizer_type_Instruction_TypeObject, &instr, &instrOffset, &rabbitizer_type_Instruction_TypeObject, &pyPrevInstr)) {
+    if (!PyArg_ParseTupleAndKeywords(args, kwds, "O!i|O&", kwlist, &rabbitizer_type_Instruction_TypeObject, &instr, &instrOffset, rabbitizer_converter_InstructionOrNone, &pyPrevInstr)) {
         return NULL;
     }