diff --git a/decor/percentage.go b/decor/percentage.go
index e1d45c9..aadd71b 100644
--- a/decor/percentage.go
+++ b/decor/percentage.go
@@ -6,6 +6,8 @@
 
 	"github.com/vbauerster/mpb/v8/internal"
 )
+
+var _ fmt.Formatter = percentageType(0)
 
 type percentageType float64
 
diff --git a/decor/size_type.go b/decor/size_type.go
index 5b64ef9..232788e 100644
--- a/decor/size_type.go
+++ b/decor/size_type.go
@@ -7,6 +7,11 @@
 
 //go:generate stringer -type=SizeB1024 -trimprefix=_i
 //go:generate stringer -type=SizeB1000 -trimprefix=_
+
+var (
+	_ fmt.Formatter = SizeB1024(0)
+	_ fmt.Formatter = SizeB1000(0)
+)
 
 const (
 	_ib   SizeB1024 = iota + 1