diff --git a/completions/useradd b/completions/useradd
index 33c41c60f6a..4216e71d353 100644
--- a/completions/useradd
+++ b/completions/useradd
@@ -24,7 +24,8 @@ _useradd()
             return 0
             ;;
         -G|--groups)
-            COMPREPLY=( $( compgen -g -- "$cur" ) )
+            local prefix=; [[ $cur == *,* ]] && prefix="${cur%,*},"
+            COMPREPLY=( $( compgen -P "$prefix" -g -- "${cur##*,}" ) )
             return 0
             ;;
         -s|--shell)
diff --git a/completions/usermod b/completions/usermod
index f8cd9e0e5d7..8999c6feac7 100644
--- a/completions/usermod
+++ b/completions/usermod
@@ -20,7 +20,8 @@ _usermod()
             return 0
             ;;
         -G|--groups)
-            COMPREPLY=( $( compgen -g -- "$cur" ) )
+            local prefix=; [[ $cur == *,* ]] && prefix="${cur%,*},"
+            COMPREPLY=( $( compgen -P "$prefix" -g -- "${cur##*,}" ) )
             return 0
             ;;
         -s|--shell)