diff --git a/b2/chr.c b/b2/chr.c
index 1b68572..ecad525 100644
--- a/b2/chr.c
+++ b/b2/chr.c
@@ -141,9 +141,11 @@ static void dump_field_decl(FILE *file, const struct field *field)
 	else if (field->fmt->ops == &param_ops_set)
 		dump_set_decl(file, field->fmt->u.set);
 	else if (field->fmt->ops == &param_ops_abs)
-		fprintf(file, "#%s", field->fmt->u.abs);
+		fprintf(file, "#%s",
+		    field->fmt->u.abs ? field->fmt->u.abs : "#");
 	else if (field->fmt->ops == &param_ops_rel)
-		fprintf(file, "%%%s", field->fmt->u.rel->u.abs);
+		fprintf(file, "%%%s",
+		    field->fmt->u.rel->u.abs ? field->fmt->u.rel->u.abs : "#");
 	else
 		abort();
 }
diff --git a/b2/dump.c b/b2/dump.c
index 31d3f8b..b4e9f2a 100644
--- a/b2/dump.c
+++ b/b2/dump.c
@@ -43,7 +43,7 @@ void dump_set(FILE *file, const struct format *fmt, const struct value *v)
 
 void dump_abs(FILE *file, const struct format *fmt, const struct value *v)
 {
-	fprintf(file, "%g%s", v->u.abs, fmt->u.abs);
+	fprintf(file, "%g%s", v->u.abs, fmt->u.abs ? fmt->u.abs : "");
 }
 
 
@@ -54,7 +54,8 @@ void dump_rel(FILE *file, const struct format *fmt, const struct value *v)
 		    v->u.rel.minus*100, v->u.rel.plus*100);
 	else
 		fprintf(file, "-%g/+%g%s",
-		    v->u.rel.minus, v->u.rel.plus, fmt->u.rel->u.abs);
+		    v->u.rel.minus, v->u.rel.plus,
+		    fmt->u.rel->u.abs ? fmt->u.rel->u.abs : "");
 }
 
 
diff --git a/b2/eval.c b/b2/eval.c
index 9cfa4c1..5163c77 100644
--- a/b2/eval.c
+++ b/b2/eval.c
@@ -92,11 +92,13 @@ static int strip_unit(const char *s, const char **stop, const char *unit,
 {
 	int n;
 
-	n = strlen(unit);
-	if (*stop-n < s)
-		return 0;
-	if (!strcmp(*stop-n, unit))
-		*stop -= n;
+	if (unit) {
+		n = strlen(unit);
+		if (*stop-n < s)
+			return 0;
+		if (!strcmp(*stop-n, unit))
+			*stop -= n;
+	}
 	if (*stop > s) {
 		if (decode_mult((*stop)[-1], mult))
 			(*stop)--;
diff --git a/b2/lang.y b/b2/lang.y
index b1e87c3..3f79991 100644
--- a/b2/lang.y
+++ b/b2/lang.y
@@ -393,6 +393,12 @@ format:
 			$$->ops = &param_ops_abs;
 			$$->u.abs = $2;
 		}
+	| '#' '#'
+		{
+			$$ = alloc_type(struct format);
+			$$->ops = &param_ops_abs;
+			$$->u.abs = NULL;
+		}
 	| '%' WORD
 		{
 			$$ = alloc_type(struct format);
diff --git a/b2/param.h b/b2/param.h
index a4d884a..9f74bd3 100644
--- a/b2/param.h
+++ b/b2/param.h
@@ -45,7 +45,7 @@ struct format {
 	const struct param_ops *ops;
 	union {
 		const struct names *set;
-		const char *abs;	/* unit name */
+		const char *abs;	/* unit name; NULL if dimensionless */
 		const struct format *rel;
 	} u;
 };
diff --git a/b2/test/hierfld b/b2/test/hierfld
index 3de01f8..b40a32f 100755
--- a/b2/test/hierfld
+++ b/b2/test/hierfld
@@ -41,7 +41,7 @@ EOF
 
 #------------------------------------------------------------------------------
 
-tst "hierarchy: absolute value field" <<EOF
+tst "hierarchy: absolute value field (with unit)" <<EOF
 { X=#foo };
 EOF
 
@@ -51,7 +51,17 @@ EOF
 
 #------------------------------------------------------------------------------
 
-tst_fail "hierarchy: absolute value field (omit type name)" <<EOF
+tst "hierarchy: absolute value field (without unit)" <<EOF
+{ X=## };
+EOF
+
+expect <<EOF
+{ X=## }
+EOF
+
+#------------------------------------------------------------------------------
+
+tst_fail "hierarchy: absolute value field (omit unit name)" <<EOF
 { X=# };
 EOF
 
diff --git a/b2/test/hierrul b/b2/test/hierrul
index 5b9cd0e..c15b59a 100755
--- a/b2/test/hierrul
+++ b/b2/test/hierrul
@@ -79,7 +79,7 @@ EOF
 
 #------------------------------------------------------------------------------
 
-tst "hierarchy: absolute value rule" <<EOF
+tst "hierarchy: absolute value rule (with unit)" <<EOF
 <predation> = mouse<cat<dog;
 N=#R {
 	10R:	{ X=* };
@@ -98,6 +98,25 @@ EOF
 
 #------------------------------------------------------------------------------
 
+tst "hierarchy: absolute value rule (without unit)" <<EOF
+<predation> = mouse<cat<dog;
+N=## {
+	2:	{ X=* };
+	5k:	{ Y=* };
+	3.1:	{ Z=* };
+};
+EOF
+
+expect <<EOF
+N=## {
+    2: { X=* }
+    5000: { Y=* }
+    3.1: { Z=* }
+}
+EOF
+
+#------------------------------------------------------------------------------
+
 tst_fail "hierarchy: absolute value rule (different unit)" <<EOF
 <predation> = mouse<cat<dog;
 N=#R {
@@ -142,7 +161,7 @@ EOF
 
 #------------------------------------------------------------------------------
 
-tst "hierarchy: relative value rule (absolute)" <<EOF
+tst "hierarchy: relative value rule (absolute, with unit)" <<EOF
 { V=#R }
 TOL=%V {
 	1R:	{ X=* };
@@ -160,6 +179,24 @@ EOF
 
 #------------------------------------------------------------------------------
 
+tst "hierarchy: relative value rule (absolute, without unit)" <<EOF
+{ V=## }
+TOL=%V {
+	1:	{ X=* };
+	1k:	{ Y=* };
+};
+EOF
+
+expect <<EOF
+{ V=## }
+TOL=%# {
+    -1/+1: { X=* }
+    -1000/+1000: { Y=* }
+}
+EOF
+
+#------------------------------------------------------------------------------
+
 tst "hierarchy: relative value rule (plus/minus percent)" <<EOF
 { V=#R }
 TOL=%V {