diff --git a/libraries/ESP8266WebServer/src/Parsing-impl.h b/libraries/ESP8266WebServer/src/Parsing-impl.h
index 8f85b7ad50..1a6a54f164 100644
--- a/libraries/ESP8266WebServer/src/Parsing-impl.h
+++ b/libraries/ESP8266WebServer/src/Parsing-impl.h
@@ -520,7 +520,7 @@ String ESP8266WebServerTemplate<ServerType>::urlDecode(const String& text)
   char temp[] = "0x00";
   unsigned int len = text.length();
   unsigned int i = 0;
-  decoded.reserve(len);
+  decoded.reserve(len - (std::count(text.begin(), text.end(), '%') * 2 ));
   while (i < len)
   {
     char decodedChar;