diff --git a/types/coin.go b/types/coin.go
index 6c95debdeb88..365e0f2efad0 100644
--- a/types/coin.go
+++ b/types/coin.go
@@ -478,7 +478,7 @@ func (coins Coins) Sort() Coins {
 
 var (
 	// Denominations can be 3 ~ 16 characters long.
-	reDnmString = `[[:lower:]][[:alnum:]]{2,15}`
+	reDnmString = `[a-z][a-z0-9]{2,15}`
 	reAmt       = `[[:digit:]]+`
 	reDecAmt    = `[[:digit:]]*\.[[:digit:]]+`
 	reSpc       = `[[:space:]]*`