diff --git a/util.go b/util.go
index b0903fb..aec8a99 100644
--- a/util.go
+++ b/util.go
@@ -41,15 +41,23 @@ func (pe ConfigParseError) Error() string {
 
 func insensitiviseMap(m map[string]interface{}) {
 	for key, val := range m {
+		switch val.(type) {
+		case map[interface{}]interface{}:
+			// nested map: cast and recursively insensitivise
+			val = cast.ToStringMap(val)
+			insensitiviseMap(val.(map[string]interface{}))
+		case map[string]interface{}:
+			// nested map: recursively insensitivise
+			insensitiviseMap(val.(map[string]interface{}))
+		}
+
 		lower := strings.ToLower(key)
 		if key != lower {
+			// remove old key (not lower-cased)
 			delete(m, key)
-			m[lower] = val
-			if m2, ok := val.(map[string]interface{}); ok {
-				// nested map: recursively insensitivise
-				insensitiviseMap(m2)
-			}
 		}
+		// update map
+		m[lower] = val
 	}
 }
 
diff --git a/viper_test.go b/viper_test.go
index 963c3ce..81c6333 100644
--- a/viper_test.go
+++ b/viper_test.go
@@ -269,7 +269,7 @@ func TestUnmarshalling(t *testing.T) {
 	assert.False(t, InConfig("state"))
 	assert.Equal(t, "steve", Get("name"))
 	assert.Equal(t, []interface{}{"skateboarding", "snowboarding", "go"}, Get("hobbies"))
-	assert.Equal(t, map[string]interface{}{"jacket": "leather", "trousers": "denim", "pants": map[interface{}]interface{}{"size": "large"}}, Get("clothing"))
+	assert.Equal(t, map[string]interface{}{"jacket": "leather", "trousers": "denim", "pants": map[string]interface{}{"size": "large"}}, Get("clothing"))
 	assert.Equal(t, 35, Get("age"))
 }
 
@@ -637,10 +637,10 @@ func TestFindsNestedKeys(t *testing.T) {
 		"age":  35,
 		"owner": map[string]interface{}{
 			"organization": "MongoDB",
-			"Bio":          "MongoDB Chief Developer Advocate & Hacker at Large",
+			"bio":          "MongoDB Chief Developer Advocate & Hacker at Large",
 			"dob":          dob,
 		},
-		"owner.Bio": "MongoDB Chief Developer Advocate & Hacker at Large",
+		"owner.bio": "MongoDB Chief Developer Advocate & Hacker at Large",
 		"type":      "donut",
 		"id":        "0001",
 		"name":      "Cake",
@@ -649,7 +649,7 @@ func TestFindsNestedKeys(t *testing.T) {
 		"clothing": map[string]interface{}{
 			"jacket":   "leather",
 			"trousers": "denim",
-			"pants": map[interface{}]interface{}{
+			"pants": map[string]interface{}{
 				"size": "large",
 			},
 		},
@@ -695,7 +695,7 @@ func TestReadBufConfig(t *testing.T) {
 	assert.False(t, v.InConfig("state"))
 	assert.Equal(t, "steve", v.Get("name"))
 	assert.Equal(t, []interface{}{"skateboarding", "snowboarding", "go"}, v.Get("hobbies"))
-	assert.Equal(t, map[string]interface{}{"jacket": "leather", "trousers": "denim", "pants": map[interface{}]interface{}{"size": "large"}}, v.Get("clothing"))
+	assert.Equal(t, map[string]interface{}{"jacket": "leather", "trousers": "denim", "pants": map[string]interface{}{"size": "large"}}, v.Get("clothing"))
 	assert.Equal(t, 35, v.Get("age"))
 }