diff --git a/src/core/thread/network_diagnostic_tlvs.hpp b/src/core/thread/network_diagnostic_tlvs.hpp
index ed46eeb8c..b27c1e2ad 100644
--- a/src/core/thread/network_diagnostic_tlvs.hpp
+++ b/src/core/thread/network_diagnostic_tlvs.hpp
@@ -164,7 +164,7 @@ public:
      * @returns The Parent Priority value.
      *
      */
-    int8_t GetParentPriority(void) const { return (mParentPriority & kParentPriorityOffset) >> kParentPriorityOffset; }
+    int8_t GetParentPriority(void) const { return (mParentPriority & kParentPriorityMask) >> kParentPriorityOffset; }
 
     /**
      * This method sets the Parent Priority value.