diff --git a/src/numpy_quaternion.c b/src/numpy_quaternion.c
index d8989f5..e5927b4 100644
--- a/src/numpy_quaternion.c
+++ b/src/numpy_quaternion.c
@@ -359,13 +359,13 @@ QQ_QS_SQ_BINARY_QUATERNION_RETURNER(power)
     Py_RETURN_NOTIMPLEMENTED; \
   }
 #define QQ_QS_SQ_BINARY_QUATERNION_INPLACE(name) QQ_QS_SQ_BINARY_QUATERNION_INPLACE_FULL(name, name)
-QQ_QS_SQ_BINARY_QUATERNION_INPLACE(add)
-QQ_QS_SQ_BINARY_QUATERNION_INPLACE(subtract)
-QQ_QS_SQ_BINARY_QUATERNION_INPLACE(multiply)
-QQ_QS_SQ_BINARY_QUATERNION_INPLACE(divide)
+/* QQ_QS_SQ_BINARY_QUATERNION_INPLACE(add) */
+/* QQ_QS_SQ_BINARY_QUATERNION_INPLACE(subtract) */
+/* QQ_QS_SQ_BINARY_QUATERNION_INPLACE(multiply) */
+/* QQ_QS_SQ_BINARY_QUATERNION_INPLACE(divide) */
 /* QQ_QS_SQ_BINARY_QUATERNION_INPLACE_FULL(true_divide, divide) */
 /* QQ_QS_SQ_BINARY_QUATERNION_INPLACE_FULL(floor_divide, divide) */
-QQ_QS_SQ_BINARY_QUATERNION_INPLACE(power)
+/* QQ_QS_SQ_BINARY_QUATERNION_INPLACE(power) */
 
 static PyObject *
 pyquaternion__reduce(PyQuaternion* self)
@@ -516,7 +516,7 @@ PyMethodDef pyquaternion_methods[] = {
 };
 
 static PyObject* pyquaternion_num_power(PyObject* a, PyObject* b, PyObject *c) { (void) c; return pyquaternion_power(a,b); }
-static PyObject* pyquaternion_num_inplace_power(PyObject* a, PyObject* b, PyObject *c) { (void) c; return pyquaternion_inplace_power(a,b); }
+/* static PyObject* pyquaternion_num_inplace_power(PyObject* a, PyObject* b, PyObject *c) { (void) c; return pyquaternion_inplace_power(a,b); } */
 static PyObject* pyquaternion_num_negative(PyObject* a) { return pyquaternion_negative(a,NULL); }
 static PyObject* pyquaternion_num_positive(PyObject* a) { return pyquaternion_positive(a,NULL); }
 static PyObject* pyquaternion_num_absolute(PyObject* a) { return pyquaternion_absolute(a,NULL); }
@@ -572,14 +572,14 @@ static PyNumberMethods pyquaternion_as_number = {
   pyquaternion_convert_oct,       // nb_oct
   pyquaternion_convert_hex,       // nb_hex
   #endif
-  pyquaternion_inplace_add,       // nb_inplace_add
-  pyquaternion_inplace_subtract,  // nb_inplace_subtract
-  pyquaternion_inplace_multiply,  // nb_inplace_multiply
+  0,                              // nb_inplace_add
+  0,                              // nb_inplace_subtract
+  0,                              // nb_inplace_multiply
   #if PY_MAJOR_VERSION < 3
-  pyquaternion_inplace_divide,    // nb_inplace_divide
+  0,                              // nb_inplace_divide
   #endif
   0,                              // nb_inplace_remainder
-  pyquaternion_num_inplace_power, // nb_inplace_power
+  0,                              // nb_inplace_power
   0,                              // nb_inplace_lshift
   0,                              // nb_inplace_rshift
   0,                              // nb_inplace_and
@@ -587,8 +587,8 @@ static PyNumberMethods pyquaternion_as_number = {
   0,                              // nb_inplace_or
   pyquaternion_divide,            // nb_floor_divide
   pyquaternion_divide,            // nb_true_divide
-  pyquaternion_inplace_divide,    // nb_inplace_floor_divide
-  pyquaternion_inplace_divide,    // nb_inplace_true_divide
+  0,                              // nb_inplace_floor_divide
+  0,                              // nb_inplace_true_divide
   0,                              // nb_index
   #if PY_MAJOR_VERSION >= 3
   #if PY_MINOR_VERSION >= 5
diff --git a/tests/test_quaternion.py b/tests/test_quaternion.py
index 72a11a8..9c410dd 100644
--- a/tests/test_quaternion.py
+++ b/tests/test_quaternion.py
@@ -776,6 +776,25 @@ def test_quaternion_add(Qs):
             assert (s + q == quaternion.quaternion(q.w + s, q.x, q.y, q.z))
 
 
+def test_quaternion_inplace_add(Qs):
+    for qo in Qs[Qs_finite]:
+        for po in Qs[Qs_finite]:
+            q = qo.copy()  # copy to prevent mutating original
+            p = po.copy()  # copy to prevent mutating original
+            q2 = q
+            q2 += p
+            assert q2 == quaternion.quaternion(qo.w + p.w, qo.x + p.x, qo.y + p.y, qo.z + p.z)
+            # Ensure value of object q has not changed
+            assert q == qo
+    for qo in Qs[Qs_nonnan]:
+        for s in [-3, -2.3, -1.2, -1.0, 0.0, 0, 1.0, 1, 1.2, 2.3, 3]:
+            q = qo.copy()  # Make copy to prevent mutating original
+            q2 = q
+            q2 += s
+            assert (q2 == quaternion.quaternion(qo.w + s, qo.x, qo.y, qo.z))
+            assert (q == qo)
+
+
 def test_quaternion_add_ufunc(Qs):
     ufunc_binary_utility(Qs[Qs_finite], Qs[Qs_finite], operator.add)
 
@@ -790,6 +809,25 @@ def test_quaternion_subtract(Qs):
             assert (s - q == quaternion.quaternion(s - q.w, -q.x, -q.y, -q.z))
 
 
+def test_quaternion_inplace_subtract(Qs):
+    for qo in Qs[Qs_finite]:
+        for po in Qs[Qs_finite]:
+            q = qo.copy()  # copy to prevent mutating original
+            p = po.copy()  # copy to prevent mutating original
+            q2 = q
+            q2 -= p
+            assert q2 == quaternion.quaternion(qo.w - p.w, qo.x - p.x, qo.y - p.y, qo.z - p.z)
+            # Ensure value of object q has not changed
+            assert q == qo
+    for qo in Qs[Qs_nonnan]:
+        for s in [-3, -2.3, -1.2, -1.0, 0.0, 0, 1.0, 1, 1.2, 2.3, 3]:
+            q = qo.copy()  # Make copy to prevent mutating original
+            q2 = q
+            q2 -= s
+            assert (q2 == quaternion.quaternion(qo.w - s, qo.x, qo.y, qo.z))
+            assert (q == qo)
+
+
 def test_quaternion_subtract_ufunc(Qs):
     ufunc_binary_utility(Qs[Qs_finite], Qs[Qs_finite], operator.sub)