diff --git a/size.go b/size.go
index 85f6ab0..0aefa73 100644
--- a/size.go
+++ b/size.go
@@ -31,7 +31,7 @@ type unitMap map[string]int64
 var (
 	decimalMap = unitMap{"k": KB, "m": MB, "g": GB, "t": TB, "p": PB}
 	binaryMap  = unitMap{"k": KiB, "m": MiB, "g": GiB, "t": TiB, "p": PiB}
-	sizeRegex  = regexp.MustCompile(`^(\d+(\.\d+)*) ?([kKmMgGtTpP])?[iI]?[bB]?$`)
+	sizeRegex  = regexp.MustCompile(`(?i)^(\d+(\.\d+)*) ?([kmgtp])?i?b?$`)
 )
 
 var decimapAbbrs = []string{"B", "kB", "MB", "GB", "TB", "PB", "EB", "ZB", "YB"}