diff --git a/httplib.h b/httplib.h
index e640670..96f73b8 100644
--- a/httplib.h
+++ b/httplib.h
@@ -11,16 +11,45 @@
 /*
  * Configuration
  */
+#ifndef CPPHTTPLIB_KEEPALIVE_TIMEOUT_SECOND
 #define CPPHTTPLIB_KEEPALIVE_TIMEOUT_SECOND 5
+#endif
+
+#ifndef CPPHTTPLIB_KEEPALIVE_TIMEOUT_USECOND
 #define CPPHTTPLIB_KEEPALIVE_TIMEOUT_USECOND 0
+#endif
+
+#ifndef CPPHTTPLIB_KEEPALIVE_MAX_COUNT
 #define CPPHTTPLIB_KEEPALIVE_MAX_COUNT 5
+#endif
+
+#ifndef CPPHTTPLIB_READ_TIMEOUT_SECOND
 #define CPPHTTPLIB_READ_TIMEOUT_SECOND 5
+#endif
+
+#ifndef CPPHTTPLIB_READ_TIMEOUT_USECOND
 #define CPPHTTPLIB_READ_TIMEOUT_USECOND 0
+#endif
+
+#ifndef CPPHTTPLIB_REQUEST_URI_MAX_LENGTH
 #define CPPHTTPLIB_REQUEST_URI_MAX_LENGTH 8192
+#endif
+
+#ifndef CPPHTTPLIB_REDIRECT_MAX_COUNT
 #define CPPHTTPLIB_REDIRECT_MAX_COUNT 20
+#endif
+
+#ifndef CPPHTTPLIB_PAYLOAD_MAX_LENGTH
 #define CPPHTTPLIB_PAYLOAD_MAX_LENGTH (std::numeric_limits<size_t>::max)()
+#endif
+
+#ifndef CPPHTTPLIB_RECV_BUFSIZ
 #define CPPHTTPLIB_RECV_BUFSIZ size_t(4096u)
+#endif
+
+#ifndef CPPHTTPLIB_THREAD_POOL_COUNT
 #define CPPHTTPLIB_THREAD_POOL_COUNT 8
+#endif
 
 #ifdef _WIN32
 #ifndef _CRT_SECURE_NO_WARNINGS