diff --git a/join.c b/join.c
index 1a08927..4c68ad3 100644
--- a/join.c
+++ b/join.c
@@ -263,7 +263,7 @@ addtospan(struct span *sp, FILE *fp, int reset)
 	char *newl = NULL;
 	size_t len, size = 0;
 
-	if ((len = getline(&newl, &size, fp)) == -1) {
+	if ((len = getline(&newl, &size, fp)) == (size_t)-1) {
 		if (ferror(fp))
 			eprintf("getline:");
 		else