diff --git a/Net/include/Poco/Net/NameValueCollection.h b/Net/include/Poco/Net/NameValueCollection.h
index 4ae9b5b81..404100890 100644
--- a/Net/include/Poco/Net/NameValueCollection.h
+++ b/Net/include/Poco/Net/NameValueCollection.h
@@ -23,6 +23,7 @@
 #include "Poco/Net/Net.h"
 #include "Poco/String.h"
 #include "Poco/ListMap.h"
+#include <cstddef>
 
 
 namespace Poco {
@@ -97,7 +98,7 @@ public:
 	bool empty() const;
 		/// Returns true iff the header does not have any content.
 
-	int size() const;
+	std::size_t size() const;
 		/// Returns the number of name-value pairs in the
 		/// collection.
 
diff --git a/Net/src/NameValueCollection.cpp b/Net/src/NameValueCollection.cpp
index df4a457cf..8f8b5f502 100644
--- a/Net/src/NameValueCollection.cpp
+++ b/Net/src/NameValueCollection.cpp
@@ -134,9 +134,9 @@ bool NameValueCollection::empty() const
 }
 
 
-int NameValueCollection::size() const
+std::size_t NameValueCollection::size() const
 {
-	return (int) _map.size();
+	return _map.size();
 }