diff --git a/ext/websocket-parser/parser.c b/ext/websocket-parser/parser.c
index d10b04d..436cb5f 100644
--- a/ext/websocket-parser/parser.c
+++ b/ext/websocket-parser/parser.c
@@ -46,7 +46,7 @@ int wsd_Parser_parse(wsd_Parser *parser, uint64_t length, uint8_t *data)
 
     pushed = wsd_ReadBuffer_push(parser->buffer, length, data);
     if (pushed != length) {
-        wsd_Parser_error(parser, WSD_UNEXPECTED_CONDITION, "Failed to push chunk[%llu] to read buffer", length);
+        wsd_Parser_error(parser, WSD_UNEXPECTED_CONDITION, "Failed to push chunk[%" PRIu64 "] to read buffer", length);
     }
 
     chunk = calloc(8, sizeof(uint8_t));
@@ -148,7 +148,7 @@ uint64_t wsd_Parser_parse_payload(wsd_Parser *parser)
 
     frame->payload = calloc(n, sizeof(uint8_t));
     if (frame->payload == NULL) {
-        wsd_Parser_error(parser, WSD_UNEXPECTED_CONDITION, "Failed to allocate frame payload[%llu]", n);
+        wsd_Parser_error(parser, WSD_UNEXPECTED_CONDITION, "Failed to allocate frame payload[%" PRIu64 "]", n);
         return 0;
     }
 
diff --git a/ext/websocket-parser/parser.h b/ext/websocket-parser/parser.h
index 60e5dd7..63f881b 100644
--- a/ext/websocket-parser/parser.h
+++ b/ext/websocket-parser/parser.h
@@ -1,6 +1,8 @@
 #ifndef _wsd_parser_h
 #define _wsd_parser_h
 
+#include <inttypes.h>
+
 #ifndef _GNU_SOURCE
 #define _GNU_SOURCE
 #endif
diff --git a/ext/websocket-parser/websocket_parser.c b/ext/websocket-parser/websocket_parser.c
index 228b3ff..ce51058 100644
--- a/ext/websocket-parser/websocket_parser.c
+++ b/ext/websocket-parser/websocket_parser.c
@@ -21,7 +21,7 @@ void wsd_WebSocketParser_on_frame(VALUE self, wsd_Frame *frame)
     char *msg = NULL;
 
     printf("------------------------------------------------------------------------\n");
-    printf(" final: %d, rsv: [%d,%d,%d], opcode: %d, masked: %d, length: %llu\n",
+    printf(" final: %d, rsv: [%d,%d,%d], opcode: %d, masked: %d, length: %" PRIu64 "\n",
             frame->final, frame->rsv1, frame->rsv2, frame->rsv3,
             frame->opcode, frame->masked, frame->length);
     printf("------------------------------------------------------------------------\n");