diff --git a/writeimg.c b/writeimg.c
index f0139ad..2219acb 100644
--- a/writeimg.c
+++ b/writeimg.c
@@ -278,7 +278,11 @@ int main(int argc, char *argv[]) {
             exit(EXIT_FAILURE);
         }
 
+#ifdef __GLIBC__
         if (ioctl(fd, BLKGETSIZE64, &device_size) < 0) {
+#else /* With musl, ioctl's take ints, kheaders provide unsigned longs. Passes tests. */
+        if (ioctl(fd, (int)BLKGETSIZE64, &device_size) < 0) {
+#endif
             perror("ioctl");
             close(fd);
             exit(EXIT_FAILURE);