diff --git a/pkg/twmerge/validators.go b/pkg/twmerge/validators.go
index 24ba460..fa6b00a 100644
--- a/pkg/twmerge/validators.go
+++ b/pkg/twmerge/validators.go
@@ -76,7 +76,7 @@ func IsTshirtSize(val string) bool {
 }
 
 func IsShadow(val string) bool {
-	pattern := regexp.MustCompile(`^-?((\d+)?\.?(\d+)[a-z]+|0)_-?((\d+)?\.?(\d+)[a-z]+|0)`)
+	pattern := regexp.MustCompile(`^(inset_)?-?((\d+)?\.?(\d+)[a-z]+|0)_-?((\d+)?\.?(\d+)[a-z]+|0)`)
 	return pattern.MatchString(val)
 }