diff --git a/src/uxnasm.c b/src/uxnasm.c
index b229da3..6fc5cfb 100644
--- a/src/uxnasm.c
+++ b/src/uxnasm.c
@@ -39,7 +39,7 @@ typedef struct {
 	Uint16 llen, mlen, rlen;
 	Label labels[0x400];
 	Macro macros[0x100];
-	Reference refs[0x800];
+	Reference refs[0x1000];
 	char scope[0x40];
 } Program;
 
@@ -76,6 +76,10 @@ error(const char *name, const char *msg)
 static char *
 sublabel(char *src, char *scope, char *name)
 {
+	if(slen(scope) + slen(name) >= 0x3f) {
+		error("Sublabel length too long", name);
+		return NULL;
+	}
 	return scat(scat(scpy(scope, src, 0x40), "/"), name);
 }
 
@@ -175,12 +179,14 @@ makereference(char *scope, char *label, Uint16 addr)
 {
 	char subw[0x40], parent[0x40];
 	Reference *r;
-	if(p.rlen == 0x800)
+	if(p.rlen == 0x1000)
 		return error("References limit exceeded", label);
 	r = &p.refs[p.rlen++];
-	if(label[1] == '&')
-		scpy(sublabel(subw, scope, label + 2), r->name, 0x40);
-	else {
+	if(label[1] == '&') {
+		if(!sublabel(subw, scope, label + 2))
+			return error("Invalid sublabel", label);
+		scpy(subw, r->name, 0x40);
+	} else {
 		int pos = spos(label + 1, '/');
 		if(pos > 0) {
 			Label *l;
@@ -287,7 +293,7 @@ parse(char *w, FILE *f)
 		scpy(w + 1, p.scope, 0x40);
 		break;
 	case '&': /* sublabel */
-		if(!makelabel(sublabel(subw, p.scope, w + 1)))
+		if(!sublabel(subw, p.scope, w + 1) || !makelabel(subw))
 			return error("Invalid sublabel", w);
 		break;
 	case '#': /* literals hex */
@@ -408,6 +414,7 @@ static int
 assemble(FILE *f)
 {
 	char w[0x40];
+	p.ptr = 0x100;
 	scpy("on-reset", p.scope, 0x40);
 	while(fscanf(f, "%62s", w) == 1)
 		if(slen(w) > 0x3d || !parse(w, f))