diff --git a/mockgen/mockgen.go b/mockgen/mockgen.go
index 79cce84..cac22ff 100644
--- a/mockgen/mockgen.go
+++ b/mockgen/mockgen.go
@@ -245,7 +245,7 @@ Example:
 
 Package mode works by specifying the package and interface names.
 It is enabled by passing two non-flag arguments: an import path, and a
-comma-separated list of symbols. 
+comma-separated list of symbols.
 You can use "." to refer to the current path's package.
 Example:
 	mockgen database/sql/driver Conn,Driver
@@ -781,16 +781,20 @@ func (g *generator) getArgNames(m *model.Method, in bool) []string {
 	for i, p := range params {
 		name := p.Name
 
-		if name == "" || name == "_" || g.nameExistsAsPackage(name) {
+		if name == "" || name == "_" {
 			name = fmt.Sprintf("arg%d", i)
+		} else if g.nameExistsAsPackage(name) {
+			name = "_" + name
 		}
 		argNames[i] = name
 	}
 	if m.Variadic != nil && in {
 		name := m.Variadic.Name
 
-		if name == "" || g.nameExistsAsPackage(name) {
+		if name == "" {
 			name = fmt.Sprintf("arg%d", len(params))
+		} else if g.nameExistsAsPackage(name) {
+			name = "_" + name
 		}
 		argNames = append(argNames, name)
 	}