diff --git a/.functests b/.functests
index af989f50ff..5e3b177176 100755
--- a/.functests
+++ b/.functests
@@ -1,5 +1,8 @@
 #!/bin/bash
 
+# How-To debug functional tests:
+# SWIFT_TEST_IN_PROCESS=1 tox -e func -- --pdb test.functional.tests.TestFile.testCopy
+
 SRC_DIR=$(python -c "import os; print os.path.dirname(os.path.realpath('$0'))")
 set -e
 
diff --git a/doc/source/development_guidelines.rst b/doc/source/development_guidelines.rst
index 8097abf8b2..17e4aed984 100644
--- a/doc/source/development_guidelines.rst
+++ b/doc/source/development_guidelines.rst
@@ -132,6 +132,12 @@ tox environment::
 
     tox -e func-in-process-fast-post
 
+To debug the functional tests, use the 'in-process test' mode and pass the
+``--pdb`` flag to tox::
+
+    SWIFT_TEST_IN_PROCESS=1 tox -e func -- --pdb \
+        test.functional.tests.TestFile.testCopy
+
 The 'in-process test' mode searches for ``proxy-server.conf`` and
 ``swift.conf`` config files from which it copies config options and overrides
 some options to suit in process testing. The search will first look for config
@@ -236,4 +242,3 @@ another year added, and date ranges are not needed.::
     # implied.
     # See the License for the specific language governing permissions and
     # limitations under the License.
-