diff --git a/pointer-daemon.c b/pointer-daemon.c
--- a/pointer-daemon.c
+++ b/pointer-daemon.c
@@ -1,4 +1,5 @@
 #define _DEFAULT_SOURCE
+#include <errno.h>
 #include <linux/input-event-codes.h>
 #include <stdint.h>
 #include <stdio.h>
@@ -15,7 +16,22 @@
             version < 2 ? version : 2);
 }
 static void removed(void *data, struct wl_registry *registry, uint32_t name) {}
-int main(void) {
+static uint32_t extent(const char *arg) {
+    char *end;
+    errno = 0;
+    unsigned long value = strtoul(arg, &end, 10);
+    if (errno || end == arg || *end || value == 0 || value > UINT32_MAX) {
+        fprintf(stderr, "INVALID_EXTENT %s\n", arg);
+        exit(2);
+    }
+    return (uint32_t)value;
+}
+int main(int argc, char **argv) {
+    if (argc != 3) {
+        fprintf(stderr, "usage: pointer-daemon WIDTH HEIGHT\n");
+        return 2;
+    }
+    uint32_t width = extent(argv[1]), height = extent(argv[2]);
     struct wl_display *display=wl_display_connect(NULL);
     if (!display) return 1;
     struct wl_registry *registry=wl_display_get_registry(display);
@@ -26,14 +42,20 @@
     struct zwlr_virtual_pointer_v1 *pointer=
         zwlr_virtual_pointer_manager_v1_create_virtual_pointer(manager,NULL);
     wl_display_roundtrip(display);
-    fprintf(stderr,"POINTER_READY\n");fflush(stderr);
+    fprintf(stderr,"POINTER_READY extent=%u,%u\n",width,height);fflush(stderr);
     char line[128];
     uint32_t stamp=1000;
     while (fgets(line,sizeof(line),stdin)) {
         char action[16];int x,y;
-        if (sscanf(line,"%15s %d %d",action,&x,&y)!=3) continue;
-        fprintf(stderr,"INJECT %s %d,%d\n",action,x,y);fflush(stderr);
-        zwlr_virtual_pointer_v1_motion_absolute(pointer,stamp++,x,y,1600,600);
+        if (sscanf(line,"%15s %d %d",action,&x,&y)!=3 ||
+                (strcmp(action,"move") && strcmp(action,"left") && strcmp(action,"right")) ||
+                x < 0 || y < 0 || (uint32_t)x >= width || (uint32_t)y >= height) {
+            fprintf(stderr,"INVALID_INJECTION %s",line);fflush(stderr);
+            return 3;
+        }
+        fprintf(stderr,"INJECT %s %d,%d extent=%u,%u\n",action,x,y,width,height);
+        fflush(stderr);
+        zwlr_virtual_pointer_v1_motion_absolute(pointer,stamp++,x,y,width,height);
         zwlr_virtual_pointer_v1_frame(pointer);
         wl_display_flush(display);usleep(250000);
         if (!strcmp(action,"left") || !strcmp(action,"right")) {