diff --git a/src/fileio.c b/src/fileio.c
index a9552b5..46d364a 100644
--- a/src/fileio.c
+++ b/src/fileio.c
@@ -4568,7 +4568,7 @@
 	    c = TRUE;
 	    if (write_info.bw_conv_error_lnum != 0)
 	    {
-		int l = STRLEN(IObuff);
+		size_t l = STRLEN(IObuff);
 		vim_snprintf((char *)IObuff + l, IOSIZE - l, _(" in line %ld;"),
 			(long)write_info.bw_conv_error_lnum);
 	    }