diff --git a/lib/plat/unix/unix-file.c b/lib/plat/unix/unix-file.c
index c71c0d1e5..81cbb222e 100644
--- a/lib/plat/unix/unix-file.c
+++ b/lib/plat/unix/unix-file.c
@@ -155,11 +155,11 @@ _lws_plat_file_read(lws_fop_fd_t fop_fd, lws_filepos_t *amount,
 		*amount = 0;
 		return -1;
 	}
-	fop_fd->pos += (size_t)n;
+	fop_fd->pos = (lws_filepos_t)(fop_fd->pos + (lws_filepos_t)n);
 	lwsl_debug("%s: read %ld of req %ld, pos %ld, len %ld\n", __func__,
 			(long)n, (long)len, (long)fop_fd->pos,
 			(long)fop_fd->len);
-	*amount = (size_t)n;
+	*amount = (lws_filepos_t)n;
 
 	return 0;
 }
@@ -176,8 +176,8 @@ _lws_plat_file_write(lws_fop_fd_t fop_fd, lws_filepos_t *amount,
 		return -1;
 	}
 
-	fop_fd->pos += (size_t)n;
-	*amount = (size_t)n;
+	fop_fd->pos = (lws_filepos_t)(fop_fd->pos + (lws_filepos_t)n);
+	*amount = (lws_filepos_t)n;
 
 	return 0;
 }
diff --git a/lib/tls/tls.c b/lib/tls/tls.c
index cd7a8bbca..dfc5060f4 100644
--- a/lib/tls/tls.c
+++ b/lib/tls/tls.c
@@ -196,7 +196,7 @@ int alloc_file(struct lws_context *context, const char *filename, uint8_t **buf,
 		goto bail;
 	}
 
-	m = ftell(f);
+	m = (ssize_t)ftell(f);
 	if (m == -1l) {
 		n = 1;
 		goto bail;