diff --git a/include/binder/IBinder.h b/include/binder/IBinder.h
index 43b6543..d98d4c5 100644
--- a/include/binder/IBinder.h
+++ b/include/binder/IBinder.h
@@ -23,8 +23,12 @@
 #include <utils/Vector.h>
 
 
+// linux/binder.h already defines this, but we can't just include it from there
+// because there are host builds that include this file.
+#ifndef B_PACK_CHARS
 #define B_PACK_CHARS(c1, c2, c3, c4) \
     ((((c1)<<24)) | (((c2)<<16)) | (((c3)<<8)) | (c4))
+#endif  // B_PACK_CHARS
 
 // ---------------------------------------------------------------------------
 namespace android {