diff --git a/configure b/configure
index 51faa2712..6a3b21e65 100755
--- a/configure
+++ b/configure
@@ -703,7 +703,7 @@ UNIVERSAL_ARCHS
 startupitem_install
 MPFRAMEWORKSDIR
 MPAPPLICATIONSDIR
-MTREE_UGNAME
+MTREE_GNAME
 DSTMODE
 RUNUSR
 DSTGRP
@@ -7014,10 +7014,15 @@ printf "%s\n" "$DSTMODE" >&6; }
 	fi
 
 
-# Don't set uname or gname in .mtree files unless root
+# Don't set real uname or gname in .mtree files unless root
 # https://trac.macports.org/ticket/49501
 if test "$DSTUSR" = "root" ; then
-    MTREE_UGNAME="uname=root gname=$DSTGRP"
+    MTREE_GNAME="$DSTGRP"
+else
+    # This has to be set to something or mtree won't create any directories.
+    # It doesn't matter what it's set to for non-root though, as it can't
+    # change the ownership anyway.
+    MTREE_GNAME="admin"
 fi
 
 
diff --git a/configure.ac b/configure.ac
index ad12f7240..02144a8ea 100644
--- a/configure.ac
+++ b/configure.ac
@@ -227,12 +227,17 @@ MP_CHECK_RUNUSER
 MP_DIRECTORY_MODE
 MP_SHARED_DIRECTORY
 
-# Don't set uname or gname in .mtree files unless root
+# Don't set real uname or gname in .mtree files unless root
 # https://trac.macports.org/ticket/49501
 if test "$DSTUSR" = "root" ; then
-    MTREE_UGNAME="uname=root gname=$DSTGRP"
+    MTREE_GNAME="$DSTGRP"
+else
+    # This has to be set to something or mtree won't create any directories.
+    # It doesn't matter what it's set to for non-root though, as it can't
+    # change the ownership anyway.
+    MTREE_GNAME="admin"
 fi
-AC_SUBST(MTREE_UGNAME)
+AC_SUBST(MTREE_GNAME)
 
 # Check for default directories
 MP_PATH_APPLICATIONS
diff --git a/doc/base.mtree.in b/doc/base.mtree.in
index 08b9ee2f5..4ea754452 100644
--- a/doc/base.mtree.in
+++ b/doc/base.mtree.in
@@ -1,7 +1,7 @@
 # MacPorts filesystem hierarchy, for internal use only. Changes to this file will not stick across installations.
 #
 
-/set type=dir @MTREE_UGNAME@ mode=@DSTMODE@
+/set type=dir uname=root gname=@MTREE_GNAME@ mode=@DSTMODE@
 .
     man type=link link=share/man
     ..
diff --git a/doc/prefix.mtree.in b/doc/prefix.mtree.in
index 56aa7fe13..c30d0bbaf 100644
--- a/doc/prefix.mtree.in
+++ b/doc/prefix.mtree.in
@@ -1,6 +1,6 @@
 # MacPorts filesystem hierarchy, for internal use only. Changes to this file will not stick across installations.
 
-/set type=dir @MTREE_UGNAME@ mode=@DSTMODE@
+/set type=dir uname=root gname=@MTREE_GNAME@ mode=@DSTMODE@
 .
     bin
     ..