diff --git a/src/index.ts b/src/index.ts
index 71234b1..e6470ef 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -120,7 +120,7 @@ function applyConverters(
       meta.target as Function,
       meta.propertyName
     )
-    const isMap = typeMeta && new typeMeta.reflectedType() instanceof Map
+    const isMap = typeMeta && typeMeta.reflectedType && new typeMeta.reflectedType() instanceof Map
 
     const converter =
       converters[meta.type] || converters[cv.ValidationTypes.CUSTOM_VALIDATION]