diff --git a/Modules/_testcapimodule.c b/Modules/_testcapimodule.c
index 7e27ec4..3362454 100644
--- a/Modules/_testcapimodule.c
+++ b/Modules/_testcapimodule.c
@@ -67,38 +67,62 @@
 static PyObject*
 test_sizeof_c_types(PyObject *self)
 {
-#define CHECK_SIZEOF(EXPECTED, TYPE)         \
+#define CHECK_SIZEOF(TYPE, EXPECTED)         \
     if (EXPECTED != sizeof(TYPE))  {         \
         PyErr_Format(TestError,              \
             "sizeof(%s) = %u instead of %u", \
             #TYPE, sizeof(TYPE), EXPECTED);  \
         return (PyObject*)NULL;              \
     }
+#define IS_SIGNED(TYPE) (((TYPE)-1) < (TYPE)0)
+#define CHECK_SIGNNESS(TYPE, SIGNED)         \
+    if (IS_SIGNED(TYPE) != SIGNED) {         \
+        PyErr_Format(TestError,              \
+            "%s signness is, instead of %i",  \
+            #TYPE, IS_SIGNED(TYPE), SIGNED); \
+        return (PyObject*)NULL;              \
+    }
 
     /* integer types */
-    CHECK_SIZEOF(1, Py_UCS1);
-    CHECK_SIZEOF(2, Py_UCS2);
-    CHECK_SIZEOF(4, Py_UCS4);
+    CHECK_SIZEOF(Py_UCS1, 1);
+    CHECK_SIZEOF(Py_UCS2, 2);
+    CHECK_SIZEOF(Py_UCS4, 4);
+    CHECK_SIGNNESS(Py_UCS1, 0);
+    CHECK_SIGNNESS(Py_UCS2, 0);
+    CHECK_SIGNNESS(Py_UCS4, 0);
 #ifdef HAVE_INT32_T
-    CHECK_SIZEOF(4, PY_INT32_T);
+    CHECK_SIZEOF(PY_INT32_T, 4);
+    CHECK_SIGNNESS(PY_INT32_T, 1);
 #endif
 #ifdef HAVE_UINT32_T
-    CHECK_SIZEOF(4, PY_UINT32_T);
+    CHECK_SIZEOF(PY_UINT32_T, 4);
+    CHECK_SIGNNESS(PY_UINT32_T, 0);
 #endif
 #ifdef HAVE_INT64_T
-    CHECK_SIZEOF(8, PY_INT64_T);
+    CHECK_SIZEOF(PY_INT64_T, 8);
+    CHECK_SIGNNESS(PY_INT64_T, 1);
 #endif
 #ifdef HAVE_UINT64_T
-    CHECK_SIZEOF(8, PY_UINT64_T);
+    CHECK_SIZEOF(PY_UINT64_T, 8);
+    CHECK_SIGNNESS(PY_UINT64_T, 0);
 #endif
 
     /* pointer/size types */
-    CHECK_SIZEOF(sizeof(void *), size_t);
-    CHECK_SIZEOF(sizeof(void *), Py_ssize_t);
+    CHECK_SIZEOF(size_t, sizeof(void *));
+    CHECK_SIGNNESS(size_t, 0);
+    CHECK_SIZEOF(Py_ssize_t, sizeof(void *));
+    CHECK_SIGNNESS(Py_ssize_t, 1);
+
+    CHECK_SIZEOF(Py_uintptr_t, sizeof(void *));
+    CHECK_SIGNNESS(Py_uintptr_t, 0);
+    CHECK_SIZEOF(Py_intptr_t, sizeof(void *));
+    CHECK_SIGNNESS(Py_intptr_t, 1);
 
     Py_INCREF(Py_None);
     return Py_None;
 
+#undef IS_SIGNED
+#undef CHECK_SIGNESS
 #undef CHECK_SIZEOF
 }