diff --git a/src/core/pbuf.c b/src/core/pbuf.c
index 40378422..7b3f176d 100644
--- a/src/core/pbuf.c
+++ b/src/core/pbuf.c
@@ -271,7 +271,7 @@ pbuf_alloc(pbuf_layer layer, u16_t length, pbuf_type type)
       break;
     }
     case PBUF_RAM: {
-      u16_t payload_len = (u16_t)(LWIP_MEM_ALIGN_SIZE(offset) + LWIP_MEM_ALIGN_SIZE(length));
+      mem_size_t payload_len = (mem_size_t)(LWIP_MEM_ALIGN_SIZE(offset) + LWIP_MEM_ALIGN_SIZE(length));
       mem_size_t alloc_len = (mem_size_t)(LWIP_MEM_ALIGN_SIZE(SIZEOF_STRUCT_PBUF) + payload_len);
 
       /* bug #50040: Check for integer overflow when calculating alloc_len */