diff --git a/Source/exehead/fileform.c b/Source/exehead/fileform.c
index 5e4fc3f991..b78329cbb5 100644
--- a/Source/exehead/fileform.c
+++ b/Source/exehead/fileform.c
@@ -362,8 +362,8 @@ const TCHAR * NSISCALL loadHeaders(int cl_flags)
   return 0;
 }
 
-#define IBUFSIZE 16384
-#define OBUFSIZE 32768
+#define IBUFSIZE (256 * 1024)
+#define OBUFSIZE (256 * 1024)
 
 // returns -3 if compression error/eof/etc