diff --git a/altsrc/map_input_source.go b/altsrc/map_input_source.go
index 661b7856d4..117461f5a0 100644
--- a/altsrc/map_input_source.go
+++ b/altsrc/map_input_source.go
@@ -16,6 +16,11 @@ type MapInputSource struct {
 	valueMap map[interface{}]interface{}
 }
 
+// NewMapInputSource creates a new MapInputSource for implementing custom input sources.
+func NewMapInputSource(file string, valueMap map[interface{}]interface{}) *MapInputSource {
+	return &MapInputSource{file: file, valueMap: valueMap}
+}
+
 // nestedVal checks if the name has '.' delimiters.
 // If so, it tries to traverse the tree by the '.' delimited sections to find
 // a nested value for the key.
diff --git a/altsrc/map_input_source_test.go b/altsrc/map_input_source_test.go
index 5046d1485d..b90f796b30 100644
--- a/altsrc/map_input_source_test.go
+++ b/altsrc/map_input_source_test.go
@@ -6,14 +6,13 @@ import (
 )
 
 func TestMapDuration(t *testing.T) {
-	inputSource := &MapInputSource{
-		file: "test",
-		valueMap: map[interface{}]interface{}{
+	inputSource := NewMapInputSource(
+		"test",
+		map[interface{}]interface{}{
 			"duration_of_duration_type": time.Minute,
 			"duration_of_string_type":   "1m",
 			"duration_of_int_type":      1000,
-		},
-	}
+		})
 	d, err := inputSource.Duration("duration_of_duration_type")
 	expect(t, time.Minute, d)
 	expect(t, nil, err)