diff --git a/sbin/nvmecontrol/identify.c b/sbin/nvmecontrol/identify.c
index cd1d74635795..c4055088860c 100644
--- a/sbin/nvmecontrol/identify.c
+++ b/sbin/nvmecontrol/identify.c
@@ -200,6 +200,10 @@ identify_ctrlr(int argc, char *argv[])
 		}
 	}
 
+	/* Check that a controller was specified. */
+	if (optind >= argc)
+		identify_usage();
+
 	open_dev(argv[optind], &fd, 1, 1);
 	read_controller_data(fd, &cdata);
 	close(fd);
@@ -245,6 +249,10 @@ identify_ns(int argc, char *argv[])
 		}
 	}
 
+	/* Check that a namespace was specified. */
+	if (optind >= argc)
+		identify_usage();
+
 	/*
 	 * Check if the specified device node exists before continuing.
 	 *  This is a cleaner check for cases where the correct controller
diff --git a/sbin/nvmecontrol/nvmecontrol.c b/sbin/nvmecontrol/nvmecontrol.c
index af5e148ece08..b95ff3231ba8 100644
--- a/sbin/nvmecontrol/nvmecontrol.c
+++ b/sbin/nvmecontrol/nvmecontrol.c
@@ -126,10 +126,22 @@ open_dev(const char *str, int *fd, int show_error, int exit_on_error)
 	struct stat	devstat;
 	char		full_path[64];
 
+	if (!strnstr(str, NVME_CTRLR_PREFIX, strlen(NVME_CTRLR_PREFIX))) {
+		if (show_error)
+			fprintf(stderr,
+			    "Controller/namespace IDs must begin with '%s'.\n",
+			    NVME_CTRLR_PREFIX);
+		if (exit_on_error)
+			exit(EX_USAGE);
+		else
+			return (EX_USAGE);
+	}
+
 	snprintf(full_path, sizeof(full_path), "/dev/%s", str);
 	if (stat(full_path, &devstat) != 0) {
 		if (show_error)
-			fprintf(stderr, "error\n");
+			fprintf(stderr, "Could not stat %s. errno=%d (%s)\n",
+			    full_path, errno, strerror(errno));
 		if (exit_on_error)
 			exit(EX_NOINPUT);
 		else
@@ -139,8 +151,8 @@ open_dev(const char *str, int *fd, int show_error, int exit_on_error)
 	*fd = open(full_path, O_RDWR);
 	if (*fd < 0) {
 		if (show_error)
-			printf("Could not open %s. errno=%d (%s)\n", full_path,
-			    errno, strerror(errno));
+			fprintf(stderr, "Could not open %s. errno=%d (%s)\n",
+			    full_path, errno, strerror(errno));
 		if (exit_on_error)
 			exit(EX_NOPERM);
 		else
diff --git a/sbin/nvmecontrol/reset.c b/sbin/nvmecontrol/reset.c
index f19714579d96..a96722c31470 100644
--- a/sbin/nvmecontrol/reset.c
+++ b/sbin/nvmecontrol/reset.c
@@ -60,6 +60,10 @@ reset(int argc, char *argv[])
 		}
 	}
 
+	/* Check that a controller was specified. */
+	if (optind >= argc)
+		reset_usage();
+
 	open_dev(argv[optind], &fd, 1, 1);
 	if (ioctl(fd, NVME_RESET_CONTROLLER) < 0) {
 		printf("Reset request to %s failed. errno=%d (%s)\n",