diff --git a/Lib/ctypes/__init__.py b/Lib/ctypes/__init__.py
index ef90bc7..7ad9e2b 100644
--- a/Lib/ctypes/__init__.py
+++ b/Lib/ctypes/__init__.py
@@ -485,7 +485,7 @@
 def cast(obj, typ):
     return _cast(obj, obj, typ)
 
-_string_at = CFUNCTYPE(py_object, c_void_p, c_int)(_string_at_addr)
+_string_at = PYFUNCTYPE(py_object, c_void_p, c_int)(_string_at_addr)
 def string_at(ptr, size=-1):
     """string_at(addr[, size]) -> string
 
@@ -497,7 +497,7 @@
 except ImportError:
     pass
 else:
-    _wstring_at = CFUNCTYPE(py_object, c_void_p, c_int)(_wstring_at_addr)
+    _wstring_at = PYFUNCTYPE(py_object, c_void_p, c_int)(_wstring_at_addr)
     def wstring_at(ptr, size=-1):
         """wstring_at(addr[, size]) -> string
 
diff --git a/Misc/NEWS b/Misc/NEWS
index 954ae7e..82c579d 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -77,6 +77,10 @@
 Library
 -------
 
+- Issue #3554: ctypes.string_at and ctypes.wstring_at did call Python
+  api functions without holding the GIL, which could lead to a fatal
+  error when they failed.
+
 - Issue #2234: distutils failed for some versions of the cygwin compiler. The
   version reported by these tools does not necessarily follow the python
   version numbering scheme, so the module is less strict when parsing it.