diff --git a/src/modbus-private.h b/src/modbus-private.h
index ea83187..db5a3dc 100644
--- a/src/modbus-private.h
+++ b/src/modbus-private.h
@@ -14,7 +14,9 @@
 #else
 # include "stdint.h"
 # include <time.h>
+# ifndef ssize_t
 typedef int ssize_t;
+# endif
 #endif
 // clang-format on
 #include <config.h>