Some old kernel headers don't #include BLKSSZGET in sys/mount.h.
diff --git a/include/platform.h b/include/platform.h
index 636c1a5..7157f8a 100644
--- a/include/platform.h
+++ b/include/platform.h
@@ -222,6 +222,9 @@
 
 #if defined(__linux__)
 #include <sys/mount.h>
+#if !defined(BLKSSZGET)
+#define BLKSSZGET _IO(0x12, 104)
+#endif
 #if !defined(BLKGETSIZE64)
 #define BLKGETSIZE64 _IOR(0x12,114,size_t)
 #endif