diff --git a/lua_cjson.c b/lua_cjson.c
index 22f33f12..9d41d0b8 100644
--- a/lua_cjson.c
+++ b/lua_cjson.c
@@ -65,15 +65,33 @@
 #define isinf(x) (!isnan(x) && isnan((x) - (x)))
 #endif
 
+#ifndef DEFAULT_SPARSE_CONVERT
 #define DEFAULT_SPARSE_CONVERT 0
+#endif
+#ifndef DEFAULT_SPARSE_RATIO
 #define DEFAULT_SPARSE_RATIO 2
+#endif
+#ifndef DEFAULT_SPARSE_SAFE
 #define DEFAULT_SPARSE_SAFE 10
+#endif
+#ifndef DEFAULT_ENCODE_MAX_DEPTH
 #define DEFAULT_ENCODE_MAX_DEPTH 1000
+#endif
+#ifndef DEFAULT_DECODE_MAX_DEPTH
 #define DEFAULT_DECODE_MAX_DEPTH 1000
+#endif
+#ifndef DEFAULT_ENCODE_INVALID_NUMBERS
 #define DEFAULT_ENCODE_INVALID_NUMBERS 0
+#endif
+#ifndef DEFAULT_DECODE_INVALID_NUMBERS
 #define DEFAULT_DECODE_INVALID_NUMBERS 1
+#endif
+#ifndef DEFAULT_ENCODE_KEEP_BUFFER
 #define DEFAULT_ENCODE_KEEP_BUFFER 1
+#endif
+#ifndef DEFAULT_ENCODE_NUMBER_PRECISION
 #define DEFAULT_ENCODE_NUMBER_PRECISION 14
+#endif
 
 #ifdef DISABLE_INVALID_NUMBERS
 #undef DEFAULT_DECODE_INVALID_NUMBERS