diff --git a/pandas/index.pyx b/pandas/index.pyx
index 9be7e7404f3fe..bed385a9ad6aa 100644
--- a/pandas/index.pyx
+++ b/pandas/index.pyx
@@ -87,6 +87,7 @@ cdef class IndexEngine:
 
         self.initialized = 0
         self.monotonic_check = 0
+        self.unique_check = 0
 
         self.unique = 0
         self.monotonic_inc = 0
@@ -269,7 +270,7 @@ cdef class IndexEngine:
 
         if len(self.mapping) == len(values):
             self.unique = 1
-            self.unique_check = 1
+        self.unique_check = 1
 
         self.initialized = 1