diff --git a/characteristic_types.go b/characteristic_types.go
index 26c87d1..2c5b1c4 100644
--- a/characteristic_types.go
+++ b/characteristic_types.go
@@ -79,7 +79,7 @@ func (c CharacteristicTypeService) list(val *url.Values) (entity, error) {
 
 	sql += " GROUP BY ct.id;"
 
-	var characteristic_types CharacteristicTypes
+	characteristic_types := make(CharacteristicTypes, 0)
 	err := DBH.Select(&characteristic_types, sql, vals...)
 	if err != nil {
 		return nil, err
diff --git a/characteristics.go b/characteristics.go
index dedc647..8070765 100644
--- a/characteristics.go
+++ b/characteristics.go
@@ -83,7 +83,7 @@ func (c CharacteristicService) list(val *url.Values) (entity, error) {
 
 	sql += " GROUP BY c.id;"
 
-	var characteristics Characteristics
+	characteristics := make(Characteristics, 0)
 	err := DBH.Select(&characteristics, sql, vals...)
 	if err != nil {
 		return nil, err
diff --git a/measurements.go b/measurements.go
index 7c29205..ec1082e 100644
--- a/measurements.go
+++ b/measurements.go
@@ -126,7 +126,7 @@ func (m MeasurementService) list(val *url.Values) (entity, error) {
 
 	sql += ";"
 
-	var measurements Measurements
+	measurements := make(Measurements, 0)
 	err := DBH.Select(&measurements, sql, vals...)
 	if err != nil {
 		return nil, err
diff --git a/species.go b/species.go
index f24900d..2003447 100644
--- a/species.go
+++ b/species.go
@@ -99,7 +99,7 @@ func (s SpeciesService) list(val *url.Values) (entity, error) {
 
 	sql += " GROUP BY sp.id, g.genus_name;"
 
-	var species ManySpecies
+	species := make(ManySpecies, 0)
 	err := DBH.Select(&species, sql, vals...)
 	if err != nil {
 		return nil, err
diff --git a/strains.go b/strains.go
index cc6843e..43c5ccb 100644
--- a/strains.go
+++ b/strains.go
@@ -101,7 +101,7 @@ func (s StrainService) list(val *url.Values) (entity, error) {
 
 	sql += " GROUP BY st.id, st.species_id;"
 
-	var strains Strains
+	strains := make(Strains, 0)
 	err := DBH.Select(&strains, sql, vals...)
 	if err != nil {
 		return nil, err