diff --git a/b2/bom.c b/b2/bom.c
index a7ea0d5..89cb31a 100644
--- a/b2/bom.c
+++ b/b2/bom.c
@@ -11,6 +11,7 @@
 
 
 #include <stdlib.h>
+#include <stdio.h>
 #include <string.h>
 #include <ctype.h>
 #include <assert.h>
@@ -24,6 +25,9 @@
 #include "bom.h"
 
 
+#define	INDENT 4
+
+
 struct bom *bom = NULL;
 int n_bom = 0;
 
@@ -149,3 +153,26 @@ int bom_subst(struct bom *b, const struct subst *sub)
 		n_bom--;
 	return res;
 }
+
+
+void bom_dump(FILE *file, const struct bom *b)
+{
+	const char **f;
+	const struct param *var;
+
+	fprintf(file, "%s (%s)\n", b->ref, b->sym ? b->sym : "?");
+	fprintf(file, "%*s", INDENT, "");
+	for (f = b->fields; f != b->fields+b->n_fields; f++)
+		fprintf(file, "%s%s", f == b->fields ? "" : " ",
+		    **f ? *f : "-");
+	fprintf(file, "\n");
+	if (!b->vars)
+		return;
+	fprintf(file, "%*s", INDENT, "");
+	for (var = b->vars; var; var = var->next) {
+		fprintf(file, "%s%s", var == b->vars ? "" : " ", var->u.name);
+		dump_relop(file, var->op);
+		fprintf(file, "%s", var->value.u.s);
+	}
+	fprintf(file, "\n");
+}
diff --git a/b2/bom.h b/b2/bom.h
index 19e0c5b..4ef6715 100644
--- a/b2/bom.h
+++ b/b2/bom.h
@@ -13,6 +13,8 @@
 #ifndef BOM_H
 #define	BOM_H
 
+#include <stdio.h>
+
 #include "param.h"
 #include "subst.h"
 
@@ -32,5 +34,6 @@ extern int n_bom;
 struct bom *bom_parse_line(const char *s);
 void bom_set_sym(const char *ref, const char *sym);
 int bom_subst(struct bom *b, const struct subst *sub);
+void bom_dump(FILE *file, const struct bom *b);
 
 #endif /* !BOM_H */
diff --git a/b2/lang.l b/b2/lang.l
index aa8ee99..280c789 100644
--- a/b2/lang.l
+++ b/b2/lang.l
@@ -110,6 +110,7 @@ static void process_bom_line(const char *s)
 
 	b = bom_parse_line(s);
 	bom_subst(b, substitutions);
+	bom_dump(stderr, b);
 }
 
 %}