diff --git a/tcl/init.tcl.in b/tcl/init.tcl.in
index 36b911cc..840dc6f6 100644
--- a/tcl/init.tcl.in
+++ b/tcl/init.tcl.in
@@ -572,7 +572,7 @@ proc __initStateUsergroups {} {
    set user_group_list {}
    # parse regular "id" output to get all group, also those whose name cannot
    # be resolved or contain a space character
-   set id_out [runCommand id]
+   set id_out [runEnvCommand {LANG C} id]
    set id_out_grp_start [expr {[string first {groups=} $id_out] + 7}]
    set id_out_next_start [string first = $id_out $id_out_grp_start]
    ##nagelfar ignore #2 Badly formed if statement
diff --git a/tcl/util.tcl b/tcl/util.tcl
index 922f812e..8a65f1e1 100644
--- a/tcl/util.tcl
+++ b/tcl/util.tcl
@@ -57,6 +57,28 @@ proc listTo {lang lst {esc 1}} {
    return [join $lout { }]
 }
 
+proc runEnvCommand {env_list cmd args} {
+   # set specific env
+   set saved_env_list {}
+   foreach {var val} $env_list {
+      lappend saved_env_list $var [get-env $var <unset>]
+      set ::env($var) $val
+   }
+
+   set res [runCommand $cmd {*}$args]
+
+   # restore env
+   foreach {var val} $saved_env_list {
+      if {$val eq {<unset>}} {
+         unset ::env($var)
+      } else {
+         set ::env($var) $val
+      }
+   }
+
+   return $res
+}
+
 # find command path and remember it
 proc getCommandPath {cmd} {
    return [lindex [auto_execok $cmd] 0]
diff --git a/testsuite/modules.00-init/005-init_ts.exp b/testsuite/modules.00-init/005-init_ts.exp
index e31b5d21..705d2e60 100644
--- a/testsuite/modules.00-init/005-init_ts.exp
+++ b/testsuite/modules.00-init/005-init_ts.exp
@@ -249,8 +249,17 @@ send_user "\tX11 setup is [expr {$is_xrdb_avail ? {KO} : {OK}}]\n"
 # check if domainname binary is available on this system
 set domainname [auto_execok domainname]
 
-# display result of id command
+# ensure id command is run with POSIX locale to correctly parse it
+if {[info exists ::env(LANG)]} {
+    set ORIG_LANG $::env(LANG)
+}
+set ::env(LANG) C
 set idoutput [exec id]
+if {[info exists ORIG_LANG]} {
+    set ::env(LANG) $ORIG_LANG
+} else {
+    unset ::env(LANG)
+}
 send_user "\tid output is '$idoutput'\n"
 
 # get current working directory