diff --git a/b2/bom.c b/b2/bom.c
index 371d773..4fe7820 100644
--- a/b2/bom.c
+++ b/b2/bom.c
@@ -11,6 +11,7 @@
 
 
 #include <stdlib.h>
+#include <string.h>
 #include <ctype.h>
 
 #include "util.h"
@@ -22,17 +23,23 @@ struct bom *bom = NULL;
 int n_bom = 0;
 
 
+static struct bom *bom_find(const char *ref)
+{
+	struct bom *b;
+
+	for (b = bom; b != bom+n_bom; b++)
+		if (b->ref == ref)
+			return b;
+	return NULL;
+}
+
+
 struct bom *bom_parse_line(const char *s)
 {
 	struct bom *b;
-	const char *t;
+	const char *ref, *t;
 	char *f;
 
-	bom = realloc(bom, sizeof(struct bom)*(n_bom+1));
-	if (!bom)
-		abort();
-	b = bom+n_bom++;
-
 	if (*s++ != '|')
 		abort();
 	while (*s == ' ' || *s == '\t')
@@ -40,7 +47,17 @@ struct bom *bom_parse_line(const char *s)
 	for (t = s+1; *t && !isspace(*t); t++);
 	if (!*t)
 		yyerror("invalid BOM record (1)\n");
-	b->ref = stralloc_n(s, t-s);
+
+	ref = unique_n(s, t-s);
+	if (bom_find(ref))
+		yyerrorf("duplicate component reference %s", ref);
+
+	bom = realloc(bom, sizeof(struct bom)*(n_bom+1));
+	if (!bom)
+		abort();
+	b = bom+n_bom++;
+
+	b->ref = ref;
 	b->sym = NULL;
 	b->fields = NULL;
 	b->n_fields = 0;
diff --git a/b2/bom.h b/b2/bom.h
index 63d3f65..c8de71c 100644
--- a/b2/bom.h
+++ b/b2/bom.h
@@ -29,6 +29,6 @@ extern struct bom *bom;
 extern int n_bom;
 
 
-struct bom *bom_parse_line(const char *line);
+struct bom *bom_parse_line(const char *s);
 
 #endif /* !BOM_H */