diff --git a/copyparty/authsrv.py b/copyparty/authsrv.py
index f56d3b4c..517eb4af 100644
--- a/copyparty/authsrv.py
+++ b/copyparty/authsrv.py
@@ -99,6 +99,8 @@ SBADCFG = " ({})".format(BAD_CFG)
 
 PTN_U_GRP = re.compile(r"\$\{u(%[+-][^}]+)\}")
 PTN_G_GRP = re.compile(r"\$\{g(%[+-][^}]+)\}")
+PTN_U_ANY = re.compile(r"(\${[u][}%])")
+PTN_G_ANY = re.compile(r"(\${[g][}%])")
 PTN_SIGIL = re.compile(r"(\${[ug][}%])")
 
 
@@ -1131,6 +1133,16 @@ class AuthSrv(object):
         src0 = src  # abspath
         dst0 = dst  # vpath
 
+        zsl = []
+        for ptn, sigil in ((PTN_U_ANY, "${u}"), (PTN_G_ANY, "${g}")):
+            if bool(ptn.search(src)) != bool(ptn.search(dst)):
+                zsl.append(sigil)
+        if zsl:
+            t = "ERROR: if %s is mentioned in a volume definition, it must be included in both the filesystem-path [%s] and the volume-url [/%s]"
+            t = "\n".join([t % (x, src, dst) for x in zsl])
+            self.log(t, 1)
+            raise Exception(t)
+
         un_gn = [(un, gn) for un, gns in un_gns.items() for gn in gns]
         if not un_gn:
             # ensure volume creation if there's no users
diff --git a/tests/res/idp/3.conf b/tests/res/idp/3.conf
index 8e1fd8f8..b8d86a11 100644
--- a/tests/res/idp/3.conf
+++ b/tests/res/idp/3.conf
@@ -6,11 +6,11 @@
   idp-h-grp: x-idp-group
 
 [/vu/${u}]
-  /
+  /u${u}
   accs:
     r: ${u}
 
 [/vg/${g}]
-  /b
+  /g${g}
   accs:
     r: @${g}
diff --git a/tests/test_idp.py b/tests/test_idp.py
index 21d46758..3378d3b1 100644
--- a/tests/test_idp.py
+++ b/tests/test_idp.py
@@ -121,6 +121,8 @@ class TestVFS(unittest.TestCase):
         self.assertNodes(au.vfs.nodes["vg"], ["iga"])
         self.assertApEq(au.vfs.nodes["vu"].realpath, "")
         self.assertApEq(au.vfs.nodes["vg"].realpath, "")
+        self.assertApEq(au.vfs.nodes["vu"].nodes["iua"].realpath, "/uiua")
+        self.assertApEq(au.vfs.nodes["vg"].nodes["iga"].realpath, "/giga")
         self.assertAxs(au.vfs.axs, [])
         self.assertAxsAt(au, "vu/iua", [["iua"]])  # same as:
         self.assertAxs(self.nav(au, "vu/iua").axs, [["iua"]])