diff --git a/completion.go b/completion.go
index 8ed61f1..dc6a447 100644
--- a/completion.go
+++ b/completion.go
@@ -188,8 +188,8 @@ func (c *completion) complete(args []string) []Completion {
 		}
 
 		if argumentIsOption(arg) {
-			prefix, optname, islong := stripOptionPrefix(arg)
-			optname, _, argument := splitOption(prefix, optname, islong)
+			_, optname, islong := stripOptionPrefix(arg)
+			optname, _, argument := splitOption(optname, islong)
 
 			if argument == nil {
 				var o *Option
@@ -250,7 +250,7 @@ func (c *completion) complete(args []string) []Completion {
 	} else if argumentStartsOption(lastarg) {
 		// Complete the option
 		prefix, optname, islong := stripOptionPrefix(lastarg)
-		optname, split, argument := splitOption(prefix, optname, islong)
+		optname, split, argument := splitOption(optname, islong)
 
 		if argument == nil && !islong {
 			rname, n := utf8.DecodeRuneInString(optname)
diff --git a/optstyle_other.go b/optstyle_other.go
index f84b697..2053db9 100644
--- a/optstyle_other.go
+++ b/optstyle_other.go
@@ -43,7 +43,7 @@ func stripOptionPrefix(optname string) (prefix string, name string, islong bool)
 
 // splitOption attempts to split the passed option into a name and an argument.
 // When there is no argument specified, nil will be returned for it.
-func splitOption(prefix string, option string, islong bool) (string, string, *string) {
+func splitOption(option string, islong bool) (string, string, *string) {
 	pos := strings.Index(option, "=")
 
 	if (islong && pos >= 0) || (!islong && pos == 1) {
diff --git a/parser.go b/parser.go
index 939dd7b..f3fb650 100644
--- a/parser.go
+++ b/parser.go
@@ -279,8 +279,8 @@ func (p *Parser) ParseArgs(args []string) ([]string, error) {
 			continue
 		}
 
-		prefix, optname, islong := stripOptionPrefix(arg)
-		optname, _, argument := splitOption(prefix, optname, islong)
+		_, optname, islong := stripOptionPrefix(arg)
+		optname, _, argument := splitOption(optname, islong)
 
 		if islong {
 			err = p.parseLong(s, optname, argument)