diff --git a/applypatch/Android.mk b/applypatch/Android.mk
index a7412d2..7aed0a9 100644
--- a/applypatch/Android.mk
+++ b/applypatch/Android.mk
@@ -127,7 +127,8 @@
 # libbsdiff is compiled with -D_FILE_OFFSET_BITS=64.
 libimgdiff_cflags := \
     -Werror \
-    -D_FILE_OFFSET_BITS=64
+    -D_FILE_OFFSET_BITS=64 \
+    -DZLIB_CONST
 
 libimgdiff_static_libraries := \
     libbsdiff \