diff --git a/doc/guix.texi b/doc/guix.texi
index 40c2fe00cf..8da82b4d8d 100644
--- a/doc/guix.texi
+++ b/doc/guix.texi
@@ -11362,9 +11362,9 @@ The driver that the passdb should use.  Valid values include
 Defaults to @samp{"pam"}.
 @end deftypevr
 
-@deftypevr {@code{passdb-configuration} parameter} free-form-args args
-A list of key-value args to the passdb driver.
-Defaults to @samp{()}.
+@deftypevr {@code{passdb-configuration} parameter} space-separated-string-list args
+Space separated list of arguments to the passdb driver.
+Defaults to @samp{""}.
 @end deftypevr
 
 @end deftypevr
@@ -11381,9 +11381,9 @@ The driver that the userdb should use.  Valid values include
 Defaults to @samp{"passwd"}.
 @end deftypevr
 
-@deftypevr {@code{userdb-configuration} parameter} free-form-args args
-A list of key-value args to the userdb driver.
-Defaults to @samp{()}.
+@deftypevr {@code{userdb-configuration} parameter} space-separated-string-list args
+Space separated list of arguments to the userdb driver.
+Defaults to @samp{""}.
 @end deftypevr
 
 @deftypevr {@code{userdb-configuration} parameter} free-form-args override-fields
diff --git a/gnu/services/mail.scm b/gnu/services/mail.scm
index 05978e0068..20043d7518 100644
--- a/gnu/services/mail.scm
+++ b/gnu/services/mail.scm
@@ -160,8 +160,8 @@ (define-configuration passdb-configuration
 @samp{pam}, @samp{passwd}, @samp{shadow}, @samp{bsdauth}, and
 @samp{static}.")
   (args
-   (free-form-args '())
-   "A list of key-value args to the passdb driver."))
+   (space-separated-string-list '())
+   "Space separated list of arguments to the passdb driver."))
 
 (define (serialize-passdb-configuration field-name val)
   (format #t "passdb {\n")
@@ -178,8 +178,8 @@ (define-configuration userdb-configuration
    "The driver that the userdb should use.  Valid values include
 @samp{passwd} and @samp{static}.")
   (args
-   (free-form-args '())
-   "A list of key-value args to the userdb driver.")
+   (space-separated-string-list '())
+   "Space separated list of arguments to the userdb driver.")
   (override-fields
    (free-form-args '())
    "Override fields from passwd."))