diff --git a/Objects/complexobject.c b/Objects/complexobject.c
index 2ae8056ac61..f0f25415a78 100644
--- a/Objects/complexobject.c
+++ b/Objects/complexobject.c
@@ -950,13 +950,13 @@ complex_subtype_from_string(PyTypeObject *type, PyObject *v)
 
 	/* position on first nonblank */
 	start = s;
-	while (*s && isspace(Py_CHARMASK(*s)))
+	while (Py_ISSPACE(*s))
 		s++;
 	if (*s == '(') {
 		/* Skip over possible bracket from repr(). */
 		got_bracket = 1;
 		s++;
-		while (*s && isspace(Py_CHARMASK(*s)))
+		while (Py_ISSPACE(*s))
 			s++;
 	}
 
@@ -1038,7 +1038,7 @@ complex_subtype_from_string(PyTypeObject *type, PyObject *v)
 	}
 
 	/* trailing whitespace and closing bracket */
-	while (*s && isspace(Py_CHARMASK(*s)))
+	while (Py_ISSPACE(*s))
 		s++;
 	if (got_bracket) {
 		/* if there was an opening parenthesis, then the corresponding
@@ -1046,7 +1046,7 @@ complex_subtype_from_string(PyTypeObject *type, PyObject *v)
 		if (*s != ')')
 			goto parse_error;
 		s++;
-		while (*s && isspace(Py_CHARMASK(*s)))
+		while (Py_ISSPACE(*s))
 			s++;
 	}
 
diff --git a/Objects/floatobject.c b/Objects/floatobject.c
index 58f27e68ce9..9a0dbb33c21 100644
--- a/Objects/floatobject.c
+++ b/Objects/floatobject.c
@@ -214,7 +214,7 @@ PyFloat_FromString(PyObject *v, char **pend)
 	}
 	last = s + len;
 
-	while (*s && isspace(Py_CHARMASK(*s)))
+	while (Py_ISSPACE(*s))
 		s++;
 	/* We don't care about overflow or underflow.  If the platform
 	 * supports them, infinities and signed zeroes (on underflow) are
@@ -235,7 +235,7 @@ PyFloat_FromString(PyObject *v, char **pend)
 	}
 	/* Since end != s, the platform made *some* kind of sense out
 	   of the input.  Trust it. */
-	while (*end && isspace(Py_CHARMASK(*end)))
+	while (Py_ISSPACE(*end))
 		end++;
 	if (end != last) {
 		if (*end == '\0')
@@ -1220,7 +1220,7 @@ float_fromhex(PyObject *cls, PyObject *arg)
 	 ********************/
 
 	/* leading whitespace and optional sign */
-	while (isspace(*s))
+	while (Py_ISSPACE(*s))
 		s++;
 	if (*s == '-') {
 		s++;
@@ -1244,7 +1244,7 @@ float_fromhex(PyObject *cls, PyObject *arg)
 	s_store = s;
 	if (*s == '0') {
 		s++;
-		if (tolower(*s) == (int)'x')
+		if (*s == 'x' || *s == 'X')
 			s++;
 		else
 			s = s_store;
@@ -1274,7 +1274,7 @@ float_fromhex(PyObject *cls, PyObject *arg)
 		goto insane_length_error;
 
 	/* [p <exponent>] */
-	if (tolower(*s) == (int)'p') {
+	if (*s == 'p' || *s == 'P') {
 		s++;
 		exp_start = s;
 		if (*s == '-' || *s == '+')
@@ -1290,7 +1290,7 @@ float_fromhex(PyObject *cls, PyObject *arg)
 		exp = 0;
 
 	/* optional trailing whitespace leading to the end of the string */
-	while (isspace(*s))
+	while (Py_ISSPACE(*s))
 		s++;
 	if (s != s_end)
 		goto parse_error;
diff --git a/Python/pystrtod.c b/Python/pystrtod.c
index 30dd4e53941..9aeef2805fb 100644
--- a/Python/pystrtod.c
+++ b/Python/pystrtod.c
@@ -718,7 +718,7 @@ _PyOS_double_to_string(char *buf, size_t buf_len, double val,
 		/* Convert to upper case. */
 		char *p;
 		for (p = buf; *p; p++)
-			*p = toupper(*p);
+			*p = Py_TOUPPER(*p);
 	}
 
 	if (ptype)