diff --git a/src/include/lwip/sockets.h b/src/include/lwip/sockets.h
index 3f004d07..b6f3d524 100644
--- a/src/include/lwip/sockets.h
+++ b/src/include/lwip/sockets.h
@@ -409,7 +409,7 @@ typedef struct ipv6_mreq {
  * we restrict parameters to at most 128 bytes.
  */
 #if !defined(FIONREAD) || !defined(FIONBIO)
-#define IOCPARM_MASK    0x7fU           /* parameters must be < 128 bytes */
+#define IOCPARM_MASK    0x7fUL          /* parameters must be < 128 bytes */
 #define IOC_VOID        0x20000000UL    /* no parameters */
 #define IOC_OUT         0x40000000UL    /* copy out parameters */
 #define IOC_IN          0x80000000UL    /* copy in parameters */