diff --git a/capn.c b/capn.c
index 40690f9..9ae5633 100644
--- a/capn.c
+++ b/capn.c
@@ -187,7 +187,7 @@ end:
 
 static struct capn_segment *lookup_segment(struct capn* c, struct capn_segment *s, uint32_t id) {
 	struct capn_tree **x;
-	struct capn_segment *y;
+	struct capn_segment *y = NULL;
 
 	if (s && s->id == id)
 		return s;
@@ -196,7 +196,6 @@ static struct capn_segment *lookup_segment(struct capn* c, struct capn_segment *
 
 	if (id < c->segnum) {
 		x = &c->segtree;
-		y = NULL;
 		while (*x) {
 			y = (struct capn_segment*) *x;
 			if (id == y->id) {
@@ -207,6 +206,9 @@ static struct capn_segment *lookup_segment(struct capn* c, struct capn_segment *
 				x = &y->hdr.link[1];
 			}
 		}
+	} else {
+		/* Otherwise `x` may be uninitialized */
+		return NULL;
 	}
 
 	s = c->lookup ? c->lookup(c->user, id) : NULL;