diff --git a/viper.go b/viper.go
index 9727f48..680b331 100644
--- a/viper.go
+++ b/viper.go
@@ -742,8 +742,21 @@
 // Check to see if the key has been set in any of the data locations
 func IsSet(key string) bool { return v.IsSet(key) }
 func (v *Viper) IsSet(key string) bool {
-	t := v.Get(key)
-	return t != nil
+	path := strings.Split(key, v.keyDelim)
+
+	lcaseKey := strings.ToLower(key)
+	val := v.find(lcaseKey)
+
+	if val == nil {
+		source := v.find(strings.ToLower(path[0]))
+		if source != nil {
+			if reflect.TypeOf(source).Kind() == reflect.Map {
+				val = v.searchMap(cast.ToStringMap(source), path[1:])
+			}
+		}
+	}
+
+	return val != nil
 }
 
 // Have Viper check ENV variables for all
diff --git a/viper_test.go b/viper_test.go
index d9aae00..aa62235 100644
--- a/viper_test.go
+++ b/viper_test.go
@@ -611,6 +611,17 @@
 	assert.Equal(t, 35, v.Get("age"))
 }
 
+func TestIsSet(t *testing.T) {
+	v := New()
+	v.SetConfigType("yaml")
+	v.ReadConfig(bytes.NewBuffer(yamlExample))
+	assert.True(t, v.IsSet("clothing.jacket"))
+	assert.False(t, v.IsSet("clothing.jackets"))
+	assert.False(t, v.IsSet("helloworld"))
+	v.Set("helloworld", "fubar")
+	assert.True(t, v.IsSet("helloworld"))
+}
+
 func TestDirsSearch(t *testing.T) {
 
 	root, config, cleanup := initDirs(t)