diff --git a/config.h b/config.h
index 7d2ee7f2..7f943449 100644
--- a/config.h
+++ b/config.h
@@ -172,6 +172,19 @@ const lword LWORD_MAX = W64LIT(0xffffffffffffffff);
 		typedef word64 dword;
 	#endif
 #endif
+		
+// Handle missing ssize_t on Windows. Typedef's taken from:
+// https://msdn.microsoft.com/en-us/library/windows/desktop/aa383751%28v=vs.85%29.aspx#LONG_PTR
+#if defined(_WIN32) || defined(_WIN64)
+#  if defined(_WIN64)
+    typedef __int64 LONG_PTR; 
+#  else
+    typedef long LONG_PTR;
+#  endif
+    typedef LONG_PTR SSIZE_T;
+	typedef SSIZE_T ssize_t;
+#endif
+
 #ifndef CRYPTOPP_BOOL_SLOW_WORD64
 	#define CRYPTOPP_BOOL_SLOW_WORD64 0
 #endif