diff --git a/b2/bom.c b/b2/bom.c
index 144025b..a7ea0d5 100644
--- a/b2/bom.c
+++ b/b2/bom.c
@@ -13,9 +13,14 @@
 #include <stdlib.h>
 #include <string.h>
 #include <ctype.h>
+#include <assert.h>
 
 #include "util.h"
 #include "lang.h"
+#include "relop.h"
+#include "param.h"
+#include "subst.h"
+#include "subex.h"
 #include "bom.h"
 
 
@@ -61,6 +66,7 @@ struct bom *bom_parse_line(const char *s)
 	b->sym = NULL;
 	b->fields = NULL;
 	b->n_fields = 0;
+	b->vars = 0;
 
 	for (s = t; *t && *t != '\n'; s = t+1) {
 		while (*s == ' ' || *s == '\t')
@@ -99,3 +105,47 @@ void bom_set_sym(const char *ref, const char *sym)
 		yyerrorf("symbol is already set in \"%s\"", ref);
 	b->sym = sym;
 }
+
+
+static void add_var(struct param ***last, struct param *var)
+{
+	**last = var;
+	*last = &var->next;
+}
+
+
+int bom_subst(struct bom *b, const struct subst *sub)
+{
+	char tmp[4];
+	struct param *vars = NULL, **last = &vars;
+	struct param *out;
+	int i, res;
+
+	/* must be last, for removal with n_bom-- to work */
+	assert(b == bom+n_bom-1);
+
+	/* set input variables */
+	add_var(&last, make_var("REF", rel_eq, b->ref));
+	if (b->n_fields && *b->fields[0])
+		add_var(&last, make_var("VAL", rel_eq, b->fields[0]));
+	if (b->n_fields > 1 && *b->fields[1])
+		add_var(&last, make_var("FP", rel_eq, b->fields[1]));
+	else
+		yywarnf("\"%s\" has no footprint", b->ref);
+	for (i = 2; i != b->n_fields; i++)
+		if (*b->fields[i]) {
+			sprintf(tmp, "F%d", i-1);
+			add_var(&last, make_var(tmp, rel_eq, b->fields[i]));
+		}
+	if (b->sym)
+		add_var(&last, make_var("SYM", rel_eq, b->sym));
+
+	/* run substitutions */
+	res = substitute(sub, vars, &out);
+	free_vars(vars);
+	if (res)
+		b->vars = out;
+	else
+		n_bom--;
+	return res;
+}
diff --git a/b2/bom.h b/b2/bom.h
index 5411d41..19e0c5b 100644
--- a/b2/bom.h
+++ b/b2/bom.h
@@ -14,6 +14,7 @@
 #define	BOM_H
 
 #include "param.h"
+#include "subst.h"
 
 
 struct bom {
@@ -30,5 +31,6 @@ 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);
 
 #endif /* !BOM_H */
diff --git a/b2/lang.l b/b2/lang.l
index 97ae698..aa8ee99 100644
--- a/b2/lang.l
+++ b/b2/lang.l
@@ -103,6 +103,15 @@ void parse_symbols(const char *name)
 	do_parse(name, START_SYMBOLS, 1, 0);
 }
 
+
+static void process_bom_line(const char *s)
+{
+	struct bom *b;
+
+	b = bom_parse_line(s);
+	bom_subst(b, substitutions);
+}
+
 %}
 
 
@@ -138,7 +147,7 @@ PAT	"\\"[^\t\n]|[^ \t\n\\]
 <BOM>"eeschema \("[^\n]*	{ hash = 0;
 				  return BOM_EESCHEMA; }
 <BOM>"|"[^\n]*			{ if (hash == 1)
-					bom_parse_line(yytext); }
+					process_bom_line(yytext); }
 <BOM>"#End Cmp"			{ YY_FLUSH_BUFFER;
 				  return 0; }
 <BOM>#[^\n]*			hash++;