diff --git a/fun.go b/fun.go
index 424b021..97fdf1a 100644
--- a/fun.go
+++ b/fun.go
@@ -151,7 +151,7 @@ func xfiltrate() string {
 	return s
 }
 
-var re_hashes = regexp.MustCompile(`(?:^|\W)#[[:alnum:]-]+`)
+var re_hashes = regexp.MustCompile(`(?:^|\W)#[[:alpha:]][[:alnum:]-]*`)
 
 func ontologies(s string) []string {
 	m := re_hashes.FindAllString(s, -1)