diff --git a/CHANGELOG.rst b/CHANGELOG.rst
index 026bfcc8b41ecad91dc915351d54e19158ce3f74..2f22513656f4848cde1746f1c5554dd847affe9b 100644
--- a/CHANGELOG.rst
+++ b/CHANGELOG.rst
@@ -2,6 +2,13 @@
 =====================
 
 
+0.12.4 (Thursday 18th January 2024)
+-----------------------------------
+
+
+* Pyfeeds now sets a ``PYFEEDS_TESTING=1`` environment variable when calling
+  `feedsRun` scripts.
+
 
 0.12.3 (Friday 8th December 2023)
 ---------------------------------
diff --git a/doc/writing_a_test.md b/doc/writing_a_test.md
index 5b58775ecee96d54a0b85ff558600fffa87f27cd..4d7425d64bb5e5a07f32602adf58bcd98759c9cc 100644
--- a/doc/writing_a_test.md
+++ b/doc/writing_a_test.md
@@ -227,6 +227,12 @@ A `pyfeeds` test is called with three parameters:
      previously-generated benchmark data for the test, if it exists.
 
 
+When `pyfeeds` calls a `feedsRun` script, it sets an environment variable -
+`PYFEEDS_TESTING=1`. This may be useful for `feedsRun` scripts which are intended
+to be callable both from `pyfeeds`, and through other means, and which need to
+behave differently depending on how they are called.
+
+
 ## Writing your test in Python
 
 
diff --git a/pyfeeds/__init__.py b/pyfeeds/__init__.py
index ea50d8c9d7f9e6bb2d6b6fd5484ac0e5120dd733..89b3a488b78523f89a422e428fb9e72c0949131d 100644
--- a/pyfeeds/__init__.py
+++ b/pyfeeds/__init__.py
@@ -5,7 +5,7 @@
 # Author: Paul McCarthy <pauldmccarthy@gmail.com>
 #
 
-__version__ = '0.12.3'
+__version__ = '0.12.4'
 """The pyfeeds version number. """
 
 
diff --git a/pyfeeds/testing.py b/pyfeeds/testing.py
index aef091b34294a69c119a96e3f33c36e79436d55f..780a55ae7660963bca0163803c8c59a5ae76bd80 100644
--- a/pyfeeds/testing.py
+++ b/pyfeeds/testing.py
@@ -450,6 +450,11 @@ def runTests(pyf):
     env               = os.environ.copy()
     env['PYTHONPATH'] = op.pathsep.join([thisDir, env.get('PYTHONPATH', '')])
 
+    # set PYFEEDS_TESTING=1 in case test scripts
+    # want to know whether they are being executed
+    # by pyfeeds or via some other mechanism.
+    env['PYFEEDS_TESTING'] = '1'
+
     # For each test we store a dictionary containing
     # the results of running the test. Each result
     # dict contains: