diff --git a/gabbi/tests/gabbits_intercept/prefix.yaml b/gabbi/tests/gabbits_intercept/prefix.yaml
new file mode 100644
index 0000000..3d6d0dc
--- /dev/null
+++ b/gabbi/tests/gabbits_intercept/prefix.yaml
@@ -0,0 +1,20 @@
+
+tests:
+
+- name: provide a link
+  POST: /
+  request_headers:
+      content-type: application/json
+  data:
+      link: $ENVIRON['GABBI_PREFIX']/barnabas
+      relative: link
+
+- name: get that link
+  GET: $RESPONSE['$.link']
+  response_headers:
+      x-gabbi-url: "///[a-f0-9:-]+$ENVIRON['GABBI_PREFIX']/barnabas/"
+
+- name: get relative link
+  GET: $HISTORY['provide a link'].$RESPONSE['$.relative']
+  response_headers:
+      x-gabbi-url: "///[a-f0-9:-]+$ENVIRON['GABBI_PREFIX']/link/"
diff --git a/gabbi/utils.py b/gabbi/utils.py
index ab1f4cf..ef1462c 100644
--- a/gabbi/utils.py
+++ b/gabbi/utils.py
@@ -52,9 +52,20 @@ def create_url(base_url, host, port=None, prefix='', ssl=False):
     query_string = parsed_url.query
     path = parsed_url.path
 
-    # Guard against a prefix of None
-    if prefix:
-        path = '%s%s' % (prefix, path)
+    # Guard against a prefix of None or the url already having the
+    # prefix. Without the startswith check, the tests in prefix.yaml
+    # fail. This is a pragmatic fix which does this for any URL in a
+    # test request that does not have a scheme and does not
+    # distinguish between URLs in a gabbi test file and those
+    # generated by the server. Idealy we would not mutate nor need
+    # to check URLs returned from the server. Doing that, however,
+    # would require more complex data handling than we have now and
+    # this covers most common cases and will be okay until someone
+    # reports a bug.
+    if prefix and not path.startswith(prefix):
+        prefix = prefix.rstrip('/')
+        path = path.lstrip('/')
+        path = '%s/%s' % (prefix, path)
 
     return urlparse.urlunsplit((scheme, netloc, path, query_string, ''))
 
diff --git a/tox.ini b/tox.ini
index ec25b0a..0b3660e 100644
--- a/tox.ini
+++ b/tox.ini
@@ -8,6 +8,7 @@ deps = -r{toxinidir}/requirements.txt
        -r{toxinidir}/test-requirements.txt
 install_command = pip install -U {opts} {packages}
 commands = python setup.py testr --testr-args="{posargs}"
+setenv = GABBI_PREFIX=
 passenv = GABBI_* HOME
 
 [testenv:venv]