diff --git a/Modules/posixmodule.c b/Modules/posixmodule.c
index 73e7e60fe6..f844e07cf2 100644
--- a/Modules/posixmodule.c
+++ b/Modules/posixmodule.c
@@ -10067,7 +10067,9 @@ os_isatty_impl(PyObject *module, int fd)
 {
     int return_value;
     _Py_BEGIN_SUPPRESS_IPH
+    Py_BEGIN_ALLOW_THREADS
     return_value = isatty(fd);
+    Py_END_ALLOW_THREADS
     _Py_END_SUPPRESS_IPH
     return return_value;
 }
diff --git a/Python/fileutils.c b/Python/fileutils.c
index e8a7eda505..bf8da0599d 100644
--- a/Python/fileutils.c
+++ b/Python/fileutils.c
@@ -68,7 +68,9 @@ _Py_device_encoding(int fd)
 {
     int valid;
     _Py_BEGIN_SUPPRESS_IPH
+    Py_BEGIN_ALLOW_THREADS
     valid = isatty(fd);
+    Py_END_ALLOW_THREADS
     _Py_END_SUPPRESS_IPH
     if (!valid)
         Py_RETURN_NONE;
@@ -1776,12 +1778,22 @@ _Py_write_impl(int fd, const void *buf, size_t count, int gil_held)
 
     _Py_BEGIN_SUPPRESS_IPH
 #ifdef MS_WINDOWS
-    if (count > 32767 && isatty(fd)) {
+    if (count > 32767) {
         /* Issue #11395: the Windows console returns an error (12: not
            enough space error) on writing into stdout if stdout mode is
            binary and the length is greater than 66,000 bytes (or less,
            depending on heap usage). */
-        count = 32767;
+        if (gil_held) {
+            Py_BEGIN_ALLOW_THREADS
+            if (isatty(fd)) {
+                count = 32767;
+            }
+            Py_END_ALLOW_THREADS
+        } else {
+            if (isatty(fd)) {
+                count = 32767;
+            }
+        }
     }
 #endif
     if (count > _PY_WRITE_MAX) {