diff --git a/typescriptify/typescriptify.go b/typescriptify/typescriptify.go
index 525ee46..183eb9a 100644
--- a/typescriptify/typescriptify.go
+++ b/typescriptify/typescriptify.go
@@ -272,12 +272,13 @@ func (t *typeScriptClassBuilder) AddMapField(fieldName string, field reflect.Str
 	}
 	strippedFieldName := strings.ReplaceAll(fieldName, "?", "")
 
-	keyTypeStr := keyType.Name()
-	// Key should always be string, no need for this:
-	// _, isSimple := t.types[keyType.Kind()]
-	// if !isSimple {
-	// 	keyTypeStr = t.prefix + keyType.Name() + t.suffix
-	// }
+	var keyTypeStr string
+	mappedType, isSimple := t.types[keyType.Kind()]
+	if !isSimple {
+		keyTypeStr = t.prefix + keyType.Name() + t.suffix
+	} else {
+		keyTypeStr = t.prefix + mappedType + t.suffix
+	}
 
 	if valueType.Kind() == reflect.Struct {
 		t.fields = append(t.fields, fmt.Sprintf("%s%s: {[key: %s]: %s};", t.indent, fieldName, keyTypeStr, t.prefix+valueTypeName))
diff --git a/typescriptify/typescriptify_test.go b/typescriptify/typescriptify_test.go
index bde6225..013bde9 100644
--- a/typescriptify/typescriptify_test.go
+++ b/typescriptify/typescriptify_test.go
@@ -1076,3 +1076,27 @@ func TestTypescriptifyCustomJsonTag(t *testing.T) {
 }`
 	testConverter(t, converter, false, desiredResult, nil)
 }
+
+func TestTypescriptifyCustomTypeInMap(t *testing.T) {
+	converter := New()
+	converter.CreateConstructor = false
+
+	type Foo uint
+	converter.ManageType(reflect.TypeOf(Foo(0)), TypeOptions{TSType: "number"})
+
+	type Bar struct {
+		Foo        Foo            `json:"foo"`
+		FooInKey   map[Foo]bool   `json:"fooInKey"`
+		FooInValue map[string]Foo `json:"fooInValue"`
+	}
+
+	converter.AddType(reflect.TypeOf(Bar{}))
+
+	desiredResult := `export class Bar {
+	foo: number;
+	fooInKey: {[key: number]: boolean};
+	fooInValue: {[key: string]: number};
+}`
+
+	testConverter(t, converter, false, desiredResult, nil)
+}