diff --git a/.travis.yml b/.travis.yml
index 6e9bd3944..5dd72f6da 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -6,6 +6,7 @@ python:
   - 3.5
   - 3.6
   - 3.7
+  - 3.8
   - pypy
   - pypy3.5
 
diff --git a/bson/_cbsonmodule.c b/bson/_cbsonmodule.c
index e82e1bb34..1fbb48cc9 100644
--- a/bson/_cbsonmodule.c
+++ b/bson/_cbsonmodule.c
@@ -20,6 +20,7 @@
  * should be used to speed up BSON encoding and decoding.
  */
 
+#define PY_SSIZE_T_CLEAN
 #include "Python.h"
 #include "datetime.h"
 
@@ -1818,13 +1819,8 @@ static PyObject* _cbson_dict_to_bson(PyObject* self, PyObject* args) {
     }
 
     /* objectify buffer */
-#if PY_MAJOR_VERSION >= 3
-    result = Py_BuildValue("y#", buffer_get_buffer(buffer),
-                           buffer_get_position(buffer));
-#else
-    result = Py_BuildValue("s#", buffer_get_buffer(buffer),
-                           buffer_get_position(buffer));
-#endif
+    result = Py_BuildValue(BYTES_FORMAT_STRING, buffer_get_buffer(buffer),
+                           (Py_ssize_t)buffer_get_position(buffer));
     destroy_codec_options(&options);
     buffer_free(buffer);
     return result;
@@ -1896,7 +1892,7 @@ static PyObject* get_value(PyObject* self, PyObject* name, const char* buffer,
             if (options->is_raw_bson) {
                 value = PyObject_CallFunction(
                     options->document_class, BYTES_FORMAT_STRING "O",
-                    buffer + *position, size, options->options_obj);
+                    buffer + *position, (Py_ssize_t)size, options->options_obj);
                 if (!value) {
                     goto invalid;
                 }
@@ -2175,11 +2171,8 @@ static PyObject* get_value(PyObject* self, PyObject* name, const char* buffer,
                 goto invalid;
             }
             if ((objectid_type = _get_object(state->ObjectId, "bson.objectid", "ObjectId"))) {
-#if PY_MAJOR_VERSION >= 3
-                value = PyObject_CallFunction(objectid_type, "y#", buffer + *position, 12);
-#else
-                value = PyObject_CallFunction(objectid_type, "s#", buffer + *position, 12);
-#endif
+                value = PyObject_CallFunction(objectid_type, BYTES_FORMAT_STRING,
+                                              buffer + *position, (Py_ssize_t)12);
                 Py_DECREF(objectid_type);
             }
             *position += 12;
@@ -2365,11 +2358,8 @@ static PyObject* get_value(PyObject* self, PyObject* name, const char* buffer,
             *position += coll_length;
 
             if ((objectid_type = _get_object(state->ObjectId, "bson.objectid", "ObjectId"))) {
-#if PY_MAJOR_VERSION >= 3
-                id = PyObject_CallFunction(objectid_type, "y#", buffer + *position, 12);
-#else
-                id = PyObject_CallFunction(objectid_type, "s#", buffer + *position, 12);
-#endif
+                id = PyObject_CallFunction(objectid_type, BYTES_FORMAT_STRING,
+                                           buffer + *position, (Py_ssize_t)12);
                 Py_DECREF(objectid_type);
             }
             if (!id) {
@@ -2556,13 +2546,9 @@ static PyObject* get_value(PyObject* self, PyObject* name, const char* buffer,
                                       "Decimal128"))) {
                 value = PyObject_CallMethod(dec128,
                                             "from_bid",
-#if PY_MAJOR_VERSION >= 3
-                                            "y#",
-#else
-                                            "s#",
-#endif
+                                            BYTES_FORMAT_STRING,
                                             buffer + *position,
-                                            16);
+                                            (Py_ssize_t)16);
                 Py_DECREF(dec128);
             }
             *position += 16;
@@ -2939,7 +2925,7 @@ static PyObject* _cbson_bson_to_dict(PyObject* self, PyObject* args) {
     /* No need to decode fields if using RawBSONDocument */
     if (options.is_raw_bson) {
         result = PyObject_CallFunction(
-            options.document_class, BYTES_FORMAT_STRING "O", string, size,
+            options.document_class, BYTES_FORMAT_STRING "O", string, (Py_ssize_t)size,
             options_obj);
     }
     else {
@@ -3031,7 +3017,7 @@ static PyObject* _cbson_decode_all(PyObject* self, PyObject* args) {
         /* No need to decode fields if using RawBSONDocument. */
         if (options.is_raw_bson) {
             dict = PyObject_CallFunction(
-                options.document_class, BYTES_FORMAT_STRING "O", string, size,
+                options.document_class, BYTES_FORMAT_STRING "O", string, (Py_ssize_t)size,
                 options_obj);
         } else {
             dict = elements_to_dict(self, string + 4, (unsigned)size - 5, &options);
@@ -3143,6 +3129,7 @@ init_cbson(void)
     _cbson_API[_cbson_buffer_write_int64_INDEX] = (void *) buffer_write_int64;
     _cbson_API[_cbson_buffer_write_int32_at_position_INDEX] =
         (void *) buffer_write_int32_at_position;
+    _cbson_API[_cbson_downcast_and_check_INDEX] = (void *) _downcast_and_check;
 
 #if PY_VERSION_HEX >= 0x03010000
     /* PyCapsule is new in python 3.1 */
diff --git a/bson/_cbsonmodule.h b/bson/_cbsonmodule.h
index 237eea037..69590d564 100644
--- a/bson/_cbsonmodule.h
+++ b/bson/_cbsonmodule.h
@@ -113,8 +113,12 @@ typedef struct codec_options_t {
 #define _cbson_buffer_write_int32_at_position_RETURN void
 #define _cbson_buffer_write_int32_at_position_PROTO (buffer_t buffer, int position, int32_t data)
 
+#define _cbson_downcast_and_check_INDEX 10
+#define _cbson_downcast_and_check_RETURN int
+#define _cbson_downcast_and_check_PROTO (Py_ssize_t size, uint8_t extra)
+
 /* Total number of C API pointers */
-#define _cbson_API_POINTER_COUNT 10
+#define _cbson_API_POINTER_COUNT 11
 
 #ifdef _CBSON_MODULE
 /* This section is used when compiling _cbsonmodule */
@@ -139,6 +143,8 @@ static _cbson_buffer_write_int64_RETURN buffer_write_int64 _cbson_buffer_write_i
 
 static _cbson_buffer_write_int32_at_position_RETURN buffer_write_int32_at_position _cbson_buffer_write_int32_at_position_PROTO;
 
+static _cbson_downcast_and_check_RETURN _downcast_and_check _cbson_downcast_and_check_PROTO;
+
 #else
 /* This section is used in modules that use _cbsonmodule's API */
 
@@ -164,6 +170,8 @@ static void **_cbson_API;
 
 #define buffer_write_int32_at_position (*(_cbson_buffer_write_int32_at_position_RETURN (*)_cbson_buffer_write_int32_at_position_PROTO) _cbson_API[_cbson_buffer_write_int32_at_position_INDEX])
 
+#define _downcast_and_check (*(_cbson_downcast_and_check_RETURN (*)_cbson_downcast_and_check_PROTO) _cbson_API[_cbson_downcast_and_check_INDEX])
+
 #define _cbson_IMPORT _cbson_API = (void **)PyCapsule_Import("_cbson._C_API", 0)
 
 #endif
diff --git a/bson/time64.c b/bson/time64.c
index d9173e7f7..bad6b51dc 100644
--- a/bson/time64.c
+++ b/bson/time64.c
@@ -44,6 +44,7 @@ gmtime64_r() is a 64-bit equivalent of gmtime_r().
 #endif
 
 /* Including Python.h fixes issues with interpreters built with -std=c99. */
+#define PY_SSIZE_T_CLEAN
 #include "Python.h"
 
 #include <time.h>
diff --git a/pymongo/_cmessagemodule.c b/pymongo/_cmessagemodule.c
index 2ed23dd2c..b3a82d631 100644
--- a/pymongo/_cmessagemodule.c
+++ b/pymongo/_cmessagemodule.c
@@ -20,6 +20,7 @@
  * should be used to speed up message creation.
  */
 
+#define PY_SSIZE_T_CLEAN
 #include "Python.h"
 
 #include "_cbsonmodule.h"
@@ -37,12 +38,6 @@ struct module_state {
 static struct module_state _state;
 #endif
 
-#if PY_MAJOR_VERSION >= 3
-#define BYTES_FORMAT_STRING "y#"
-#else
-#define BYTES_FORMAT_STRING "s#"
-#endif
-
 #define DOC_TOO_LARGE_FMT "BSON document too large (%d bytes)" \
                           " - the connected server supports" \
                           " BSON document sizes up to %ld bytes."
@@ -61,10 +56,21 @@ static PyObject* _error(char* name) {
     return error;
 }
 
+/* The same as buffer_write_bytes except that it also validates
+ * "size" will fit in an int.
+ * Returns 0 on failure */
+static int buffer_write_bytes_ssize_t(buffer_t buffer, const char* data, Py_ssize_t size) {
+    int downsize = _downcast_and_check(size, 0);
+    if (size == -1) {
+        return 0;
+    }
+    return buffer_write_bytes(buffer, data, downsize);
+}
+
 /* add a lastError message on the end of the buffer.
  * returns 0 on failure */
 static int add_last_error(PyObject* self, buffer_t buffer,
-                          int request_id, char* ns, int nslen,
+                          int request_id, char* ns, Py_ssize_t nslen,
                           codec_options_t* options, PyObject* args) {
     struct module_state *state = GETSTATE(self);
 
@@ -91,8 +97,7 @@ static int add_last_error(PyObject* self, buffer_t buffer,
                             "\xd4\x07\x00\x00"  /* opcode */
                             "\x00\x00\x00\x00", /* options */
                             12) ||
-        !buffer_write_bytes(buffer,
-                            ns, nslen) ||       /* database */
+        !buffer_write_bytes_ssize_t(buffer, ns, nslen) || /* database */
         !buffer_write_bytes(buffer,
                             ".$cmd\x00"         /* collection name */
                             "\x00\x00\x00\x00"  /* skip */
@@ -142,7 +147,7 @@ static int add_last_error(PyObject* self, buffer_t buffer,
 }
 
 static int init_insert_buffer(buffer_t buffer, int request_id, int options,
-                              const char* coll_name, int coll_name_len,
+                              const char* coll_name, Py_ssize_t coll_name_len,
                               int compress) {
     int length_location = 0;
     if (!compress) {
@@ -161,9 +166,9 @@ static int init_insert_buffer(buffer_t buffer, int request_id, int options,
         }
     }
     if (!buffer_write_int32(buffer, (int32_t)options) ||
-        !buffer_write_bytes(buffer,
-                            coll_name,
-                            coll_name_len + 1)) {
+        !buffer_write_bytes_ssize_t(buffer,
+                                    coll_name,
+                                    coll_name_len + 1)) {
         return -1;
     }
     return length_location;
@@ -177,7 +182,7 @@ static PyObject* _cbson_insert_message(PyObject* self, PyObject* args) {
     /* NOTE just using a random number as the request_id */
     int request_id = rand();
     char* collection_name = NULL;
-    int collection_name_length;
+    Py_ssize_t collection_name_length;
     PyObject* docs;
     PyObject* doc;
     PyObject* iterator;
@@ -293,7 +298,7 @@ static PyObject* _cbson_insert_message(PyObject* self, PyObject* args) {
     /* objectify buffer */
     result = Py_BuildValue("i" BYTES_FORMAT_STRING "i", request_id,
                            buffer_get_buffer(buffer),
-                           buffer_get_position(buffer),
+                           (Py_ssize_t)buffer_get_position(buffer),
                            max_size);
     destroy_codec_options(&options);
     buffer_free(buffer);
@@ -306,7 +311,7 @@ static PyObject* _cbson_update_message(PyObject* self, PyObject* args) {
 
     int request_id = rand();
     char* collection_name = NULL;
-    int collection_name_length;
+    Py_ssize_t collection_name_length;
     int before, cur_size, max_size = 0;
     PyObject* doc;
     PyObject* spec;
@@ -360,9 +365,9 @@ static PyObject* _cbson_update_message(PyObject* self, PyObject* args) {
                             "\xd1\x07\x00\x00"
                             "\x00\x00\x00\x00",
                             12) ||
-        !buffer_write_bytes(buffer,
-                            collection_name,
-                            collection_name_length + 1) ||
+        !buffer_write_bytes_ssize_t(buffer,
+                                    collection_name,
+                                    collection_name_length + 1) ||
         !buffer_write_int32(buffer, (int32_t)flags)) {
         destroy_codec_options(&options);
         buffer_free(buffer);
@@ -409,7 +414,7 @@ static PyObject* _cbson_update_message(PyObject* self, PyObject* args) {
     /* objectify buffer */
     result = Py_BuildValue("i" BYTES_FORMAT_STRING "i", request_id,
                            buffer_get_buffer(buffer),
-                           buffer_get_position(buffer),
+                           (Py_ssize_t)buffer_get_position(buffer),
                            max_size);
     destroy_codec_options(&options);
     buffer_free(buffer);
@@ -424,7 +429,7 @@ static PyObject* _cbson_query_message(PyObject* self, PyObject* args) {
     PyObject* cluster_time = NULL;
     unsigned int flags;
     char* collection_name = NULL;
-    int collection_name_length;
+    Py_ssize_t collection_name_length;
     int begin, cur_size, max_size = 0;
     int num_to_skip;
     int num_to_return;
@@ -490,8 +495,8 @@ static PyObject* _cbson_query_message(PyObject* self, PyObject* args) {
     if (!buffer_write_int32(buffer, (int32_t)request_id) ||
         !buffer_write_bytes(buffer, "\x00\x00\x00\x00\xd4\x07\x00\x00", 8) ||
         !buffer_write_int32(buffer, (int32_t)flags) ||
-        !buffer_write_bytes(buffer, collection_name,
-                            collection_name_length + 1) ||
+        !buffer_write_bytes_ssize_t(buffer, collection_name,
+                                    collection_name_length + 1) ||
         !buffer_write_int32(buffer, (int32_t)num_to_skip) ||
         !buffer_write_int32(buffer, (int32_t)num_to_return)) {
         goto fail;
@@ -548,7 +553,7 @@ static PyObject* _cbson_query_message(PyObject* self, PyObject* args) {
     /* objectify buffer */
     result = Py_BuildValue("i" BYTES_FORMAT_STRING "i", request_id,
                            buffer_get_buffer(buffer),
-                           buffer_get_position(buffer),
+                           (Py_ssize_t)buffer_get_position(buffer),
                            max_size);
 
 fail:
@@ -563,7 +568,7 @@ static PyObject* _cbson_get_more_message(PyObject* self, PyObject* args) {
     /* NOTE just using a random number as the request_id */
     int request_id = rand();
     char* collection_name = NULL;
-    int collection_name_length;
+    Py_ssize_t collection_name_length;
     int num_to_return;
     long long cursor_id;
     buffer_t buffer;
@@ -597,9 +602,9 @@ static PyObject* _cbson_get_more_message(PyObject* self, PyObject* args) {
                             "\x00\x00\x00\x00"
                             "\xd5\x07\x00\x00"
                             "\x00\x00\x00\x00", 12) ||
-        !buffer_write_bytes(buffer,
-                            collection_name,
-                            collection_name_length + 1) ||
+        !buffer_write_bytes_ssize_t(buffer,
+                                    collection_name,
+                                    collection_name_length + 1) ||
         !buffer_write_int32(buffer, (int32_t)num_to_return) ||
         !buffer_write_int64(buffer, (int64_t)cursor_id)) {
         buffer_free(buffer);
@@ -616,7 +621,7 @@ static PyObject* _cbson_get_more_message(PyObject* self, PyObject* args) {
     /* objectify buffer */
     result = Py_BuildValue("i" BYTES_FORMAT_STRING, request_id,
                            buffer_get_buffer(buffer),
-                           buffer_get_position(buffer));
+                           (Py_ssize_t)buffer_get_position(buffer));
     buffer_free(buffer);
     return result;
 }
@@ -634,7 +639,7 @@ static PyObject* _cbson_op_msg(PyObject* self, PyObject* args) {
     unsigned int flags;
     PyObject* command;
     char* identifier = NULL;
-    int identifier_length = 0;
+    Py_ssize_t identifier_length = 0;
     PyObject* docs;
     PyObject* doc;
     unsigned char check_keys = 0;
@@ -696,7 +701,7 @@ static PyObject* _cbson_op_msg(PyObject* self, PyObject* args) {
         /* save space for payload 0 length */
         payload_one_length_location = buffer_save_space(buffer, 4);
         /* C string identifier */
-        if (!buffer_write_bytes(buffer, identifier, identifier_length + 1)) {
+        if (!buffer_write_bytes_ssize_t(buffer, identifier, identifier_length + 1)) {
             goto encodefail;
         }
         iterator = PyObject_GetIter(docs);
@@ -730,7 +735,7 @@ static PyObject* _cbson_op_msg(PyObject* self, PyObject* args) {
     /* objectify buffer */
     result = Py_BuildValue("i" BYTES_FORMAT_STRING "ii", request_id,
                            buffer_get_buffer(buffer),
-                           buffer_get_position(buffer),
+                           (Py_ssize_t)buffer_get_position(buffer),
                            total_size,
                            max_doc_size);
 encodefail:
@@ -763,7 +768,7 @@ _set_document_too_large(int size, long max) {
 static PyObject*
 _send_insert(PyObject* self, PyObject* ctx,
              PyObject* gle_args, buffer_t buffer,
-             char* coll_name, int coll_len, int request_id, int safe,
+             char* coll_name, Py_ssize_t coll_len, int request_id, int safe,
              codec_options_t* options, PyObject* to_publish, int compress) {
 
     if (safe) {
@@ -779,7 +784,7 @@ _send_insert(PyObject* self, PyObject* ctx,
                                "i" BYTES_FORMAT_STRING "iNOi",
                                request_id,
                                buffer_get_buffer(buffer),
-                               buffer_get_position(buffer),
+                               (Py_ssize_t)buffer_get_position(buffer),
                                0,
                                PyBool_FromLong((long)safe),
                                to_publish, compress);
@@ -792,7 +797,7 @@ static PyObject* _cbson_do_batched_insert(PyObject* self, PyObject* args) {
     int request_id = rand();
     int send_safe, flags = 0;
     int length_location, message_length;
-    int collection_name_length;
+    Py_ssize_t collection_name_length;
     int compress;
     char* collection_name = NULL;
     PyObject* docs;
@@ -1344,7 +1349,7 @@ _cbson_encode_batched_op_msg(PyObject* self, PyObject* args) {
 
     result = Py_BuildValue(BYTES_FORMAT_STRING "O",
                            buffer_get_buffer(buffer),
-                           buffer_get_position(buffer),
+                           (Py_ssize_t)buffer_get_position(buffer),
                            to_publish);
 fail:
     destroy_codec_options(&options);
@@ -1415,7 +1420,7 @@ _cbson_batched_op_msg(PyObject* self, PyObject* args) {
     buffer_write_int32_at_position(buffer, 4, (int32_t)request_id);
     result = Py_BuildValue("i" BYTES_FORMAT_STRING "O", request_id,
                            buffer_get_buffer(buffer),
-                           buffer_get_position(buffer),
+                           (Py_ssize_t)buffer_get_position(buffer),
                            to_publish);
 fail:
     destroy_codec_options(&options);
@@ -1428,7 +1433,7 @@ fail:
 
 static int
 _batched_write_command(
-        char* ns, int ns_len, unsigned char op, int check_keys,
+        char* ns, Py_ssize_t ns_len, unsigned char op, int check_keys,
         PyObject* command, PyObject* docs, PyObject* ctx,
         PyObject* to_publish, codec_options_t options,
         buffer_t buffer, struct module_state *state) {
@@ -1476,8 +1481,7 @@ _batched_write_command(
     if (!buffer_write_bytes(buffer,
                             "\x00\x00\x00\x00", /* flags */
                             4) ||
-        !buffer_write_bytes(buffer,
-                            ns, ns_len + 1) ||  /* namespace */
+        !buffer_write_bytes_ssize_t(buffer, ns, ns_len + 1) || /* namespace */
         !buffer_write_bytes(buffer,
                             "\x00\x00\x00\x00"  /* skip */
                             "\xFF\xFF\xFF\xFF", /* limit (-1) */
@@ -1634,7 +1638,7 @@ _cbson_encode_batched_write_command(PyObject* self, PyObject* args) {
     char *ns = NULL;
     unsigned char op;
     unsigned char check_keys;
-    int ns_len;
+    Py_ssize_t ns_len;
     PyObject* command;
     PyObject* docs;
     PyObject* ctx = NULL;
@@ -1677,7 +1681,7 @@ _cbson_encode_batched_write_command(PyObject* self, PyObject* args) {
 
     result = Py_BuildValue(BYTES_FORMAT_STRING "O",
                            buffer_get_buffer(buffer),
-                           buffer_get_position(buffer),
+                           (Py_ssize_t)buffer_get_position(buffer),
                            to_publish);
 fail:
     PyMem_Free(ns);
@@ -1692,7 +1696,7 @@ _cbson_batched_write_command(PyObject* self, PyObject* args) {
     char *ns = NULL;
     unsigned char op;
     unsigned char check_keys;
-    int ns_len;
+    Py_ssize_t ns_len;
     int request_id;
     int position;
     PyObject* command;
@@ -1752,7 +1756,7 @@ _cbson_batched_write_command(PyObject* self, PyObject* args) {
     buffer_write_int32_at_position(buffer, 4, (int32_t)request_id);
     result = Py_BuildValue("i" BYTES_FORMAT_STRING "O", request_id,
                            buffer_get_buffer(buffer),
-                           buffer_get_position(buffer),
+                           (Py_ssize_t)buffer_get_position(buffer),
                            to_publish);
 fail:
     PyMem_Free(ns);
diff --git a/pymongo/database.py b/pymongo/database.py
index c6900fed1..701e55221 100644
--- a/pymongo/database.py
+++ b/pymongo/database.py
@@ -823,7 +823,7 @@ class Database(common.BaseObject):
 
         For example, to list all non-system collections::
 
-            filter = {"name": {"$regex": r"^(?!system\.)"}}
+            filter = {"name": {"$regex": r"^(?!system\\.)"}}
             db.list_collection_names(filter=filter)
 
         :Parameters:
diff --git a/test/test_custom_types.py b/test/test_custom_types.py
index b0a190d0f..3d937082f 100644
--- a/test/test_custom_types.py
+++ b/test/test_custom_types.py
@@ -512,8 +512,8 @@ class TestTypeRegistry(unittest.TestCase):
 
     def test_builtin_types_override_fails(self):
         def run_test(base, attrs):
-            msg = ("TypeEncoders cannot change how built-in types "
-                   "are encoded \(encoder .* transforms type .*\)")
+            msg = (r"TypeEncoders cannot change how built-in types "
+                   r"are encoded \(encoder .* transforms type .*\)")
             for pytype in _BUILT_IN_TYPES:
                 attrs.update({'python_type': pytype,
                               'transform_python': lambda x: x})
diff --git a/test/test_database.py b/test/test_database.py
index 983bcecec..76a549c95 100644
--- a/test/test_database.py
+++ b/test/test_database.py
@@ -1062,7 +1062,7 @@ class TestDatabaseAggregation(IntegrationTest):
 
     @client_context.require_version_max(3, 6, 0, -1)
     def test_database_aggregation_unsupported(self):
-        err_msg = "Database.aggregate\(\) is only supported on MongoDB 3.6\+."
+        err_msg = r"Database.aggregate\(\) is only supported on MongoDB 3.6\+."
         with self.assertRaisesRegex(ConfigurationError, err_msg):
             with self.admin.aggregate(self.pipeline) as _:
                 pass
diff --git a/test/test_encryption.py b/test/test_encryption.py
index 58a392d69..fbd6c7010 100644
--- a/test/test_encryption.py
+++ b/test/test_encryption.py
@@ -684,8 +684,8 @@ class TestDataKeyDoubleEncryption(EncryptionIntegrationTest):
         self.assertEqual(aws_encrypted_altname, aws_encrypted)
 
         # Explicitly encrypting an auto encrypted field.
-        msg = ('Cannot encrypt element of type binData because schema '
-               'requires that type is one of: \[ string \]')
+        msg = (r'Cannot encrypt element of type binData because schema '
+               r'requires that type is one of: \[ string \]')
         with self.assertRaisesRegex(EncryptionError, msg):
             client_encrypted.db.coll.insert_one(
                 {'encrypted_placeholder': local_encrypted})
diff --git a/test/test_pooling.py b/test/test_pooling.py
index f5945a43d..922deecdc 100644
--- a/test/test_pooling.py
+++ b/test/test_pooling.py
@@ -53,7 +53,7 @@ def gc_collect_until_done(threads, timeout=60):
         assert (time.time() - start) < timeout, "Threads timed out"
         for t in running:
             t.join(0.1)
-            if not t.isAlive():
+            if not t.is_alive():
                 running.remove(t)
         gc.collect()
 
diff --git a/test/utils.py b/test/utils.py
index e308a53c6..d26b96138 100644
--- a/test/utils.py
+++ b/test/utils.py
@@ -579,7 +579,7 @@ def joinall(threads):
     """Join threads with a 5-minute timeout, assert joins succeeded"""
     for t in threads:
         t.join(300)
-        assert not t.isAlive(), "Thread %s hung" % t
+        assert not t.is_alive(), "Thread %s hung" % t
 
 
 def connected(client):
@@ -708,7 +708,7 @@ def run_threads(collection, target):
 
     for t in threads:
         t.join(60)
-        assert not t.isAlive()
+        assert not t.is_alive()
 
 
 @contextlib.contextmanager