diff --git a/changelog/4279.trivial.rst b/changelog/4279.trivial.rst
new file mode 100644
index 000000000..9f4c4c473
--- /dev/null
+++ b/changelog/4279.trivial.rst
@@ -0,0 +1 @@
+Improve message and stack level of warnings issued by ``monkeypatch.setenv`` when the value of the environment variable is not a ``str``.
diff --git a/src/_pytest/monkeypatch.py b/src/_pytest/monkeypatch.py
index 2efdb73ae..d536b7746 100644
--- a/src/_pytest/monkeypatch.py
+++ b/src/_pytest/monkeypatch.py
@@ -230,10 +230,12 @@ class MonkeyPatch(object):
         if not isinstance(value, str):
             warnings.warn(
                 pytest.PytestWarning(
-                    "Environment variable value {!r} should be str, converted to str implicitly".format(
-                        value
+                    "Value of environment variable {name} type should be str, but got "
+                    "{value!r} (type: {type}); converted to str implicitly".format(
+                        name=name, value=value, type=type(value).__name__
                     )
-                )
+                ),
+                stacklevel=2,
             )
             value = str(value)
         if prepend and name in os.environ:
diff --git a/testing/test_monkeypatch.py b/testing/test_monkeypatch.py
index d250d24e7..ebc233fbf 100644
--- a/testing/test_monkeypatch.py
+++ b/testing/test_monkeypatch.py
@@ -3,6 +3,7 @@ from __future__ import division
 from __future__ import print_function
 
 import os
+import re
 import sys
 import textwrap
 
@@ -226,9 +227,10 @@ class TestEnvironWarnings(object):
     def test_setenv_non_str_warning(self, monkeypatch):
         value = 2
         msg = (
-            "Environment variable value {!r} should be str, converted to str implicitly"
+            "Value of environment variable PYTEST_INTERNAL_MY_VAR type should be str, "
+            "but got 2 (type: int); converted to str implicitly"
         )
-        with pytest.warns(pytest.PytestWarning, match=msg.format(value)):
+        with pytest.warns(pytest.PytestWarning, match=re.escape(msg)):
             monkeypatch.setenv(str(self.VAR_NAME), value)