diff --git a/command/service/update.go b/command/service/update.go
index afa0f807e9..1933ff38eb 100644
--- a/command/service/update.go
+++ b/command/service/update.go
@@ -524,20 +524,21 @@ func updateLabels(flags *pflag.FlagSet, field *map[string]string) {
 }
 
 func updateEnvironment(flags *pflag.FlagSet, field *[]string) {
-	envSet := map[string]string{}
-	for _, v := range *field {
-		envSet[envKey(v)] = v
-	}
 	if flags.Changed(flagEnvAdd) {
+		envSet := map[string]string{}
+		for _, v := range *field {
+			envSet[envKey(v)] = v
+		}
+
 		value := flags.Lookup(flagEnvAdd).Value.(*opts.ListOpts)
 		for _, v := range value.GetAll() {
 			envSet[envKey(v)] = v
 		}
-	}
 
-	*field = []string{}
-	for _, v := range envSet {
-		*field = append(*field, v)
+		*field = []string{}
+		for _, v := range envSet {
+			*field = append(*field, v)
+		}
 	}
 
 	toRemove := buildToRemoveSet(flags, flagEnvRemove)