diff --git a/pi400.c b/pi400.c
index cb5f013..5b69be9 100644
--- a/pi400.c
+++ b/pi400.c
@@ -14,6 +14,7 @@
 #include <unistd.h>
 #include <string.h>
 #include <stdlib.h>
+#include <dirent.h>
 #include <sys/types.h>
 #include <sys/wait.h>
 
@@ -36,6 +37,24 @@ void signal_handler(int dummy) {
     running = 0;
 }
 
+void prechecks(char *argv0) {
+    DIR *dir;
+
+    if (geteuid() != 0) {
+        printf("Error: %s must be run as root.\n", argv0);
+        exit(1);
+    }
+
+    // is the 'dwc2' module properly loaded?
+    dir = opendir("/sys/module/dwc2");
+    if (!dir || errno == ENOENT) {
+        printf("Error: This must be added to /boot/config.txt and the system rebooted:\n");
+        printf("    dtoverlay=dwc2\n");
+        exit(1);
+    }
+    closedir(dir);
+}
+
 bool modprobe_libcomposite() {
     pid_t pid;
 
@@ -154,7 +173,11 @@ void send_empty_hid_reports_both() {
     }
 }
 
-int main() {
+int main(int argc, char *argv[]) {
+#ifndef NO_OUTPUT
+    prechecks(argv[0]);
+#endif
+
     modprobe_libcomposite();
 
     keyboard_buf.report_id = 1;