doc/pamtester.1.in | 4 +++-
 src/app.c          | 2 +-
 src/pamtester.c    | 7 ++++++-
 3 files changed, 10 insertions(+), 3 deletions(-)

diff --git a/doc/pamtester.1.in b/doc/pamtester.1.in
index c9b90d6..a042fab 100644
--- a/doc/pamtester.1.in
+++ b/doc/pamtester.1.in
@@ -8,7 +8,9 @@ pamtester - test pluggable authentication module (PAM) facility
 .SH DESCRIPTION
 Test pluggable authentication module (PAM) facility.
 .PP
-\fIservice\fR is the PAM service name. \fIuser\fR is the name of the user account to operate with the PAM facility. The following operations are supported.
+\fIservice\fR is the PAM service name. \fIuser\fR is the name of the user account to operate with the PAM facility. Pass "" or "NULL" to skip the user name setting.
+.PP
+The following operations are supported:
 .TP
 authenticate
 Authenticate \fIuser\fR. A conversation may subsequently take place to prompt
diff --git a/src/app.c b/src/app.c
index 9bb0aef..693bc49 100644
--- a/src/app.c
+++ b/src/app.c
@@ -210,7 +210,7 @@ int pamtester_app_run(pamtester_app_t *params)
 	}
 
 	if ((err = pam_start((params->service == NULL ? "": params->service),
-			(params->user == NULL ? "": params->user), &conv, &pamh))) {
+			params->user, &conv, &pamh))) {
 		err_msg = xstrdup("Initialization failure");
 		pamh = NULL;
 		goto out;
diff --git a/src/pamtester.c b/src/pamtester.c
index c1b143e..f962b31 100644
--- a/src/pamtester.c
+++ b/src/pamtester.c
@@ -170,7 +170,12 @@ int main(int argc, const char **argv)
 		goto out;
 	}
 
-	params.user = xstrdup(argv[op_idx++]);
+    if (0 != strcmp(argv[op_idx], "") &&
+        0 != strcmp(argv[op_idx], "NULL"))
+    {
+        params.user = xstrdup(argv[op_idx]);
+    }
+    op_idx++;
 
 	if (op_idx >= argc) {
 		fprintf(stderr, "%s: specify one or more operations.\n", prog_name);