diff --git a/cli/command/system/completion.go b/cli/command/system/completion.go
index 5665ce07dc15..d59bbed75abe 100644
--- a/cli/command/system/completion.go
+++ b/cli/command/system/completion.go
@@ -122,6 +122,7 @@ func completeFilters(dockerCLI completion.APIClientProvider) completion.ValidArg
 	}
 }
 
+// prefixWith prefixes every element in the slice with the given prefix.
 func prefixWith(prefix string, values []string) []string {
 	result := make([]string, len(values))
 	for i, v := range values {
@@ -130,6 +131,7 @@ func prefixWith(prefix string, values []string) []string {
 	return result
 }
 
+// postfixWith appends postfix to every element in the slice.
 func postfixWith(postfix string, values []string) []string {
 	result := make([]string, len(values))
 	for i, v := range values {