diff --git a/miss/miss.cpp b/miss/miss.cpp
index 648795c..635e7a5 100644
--- a/miss/miss.cpp
+++ b/miss/miss.cpp
@@ -640,7 +640,7 @@ bool IsLikelyNAT(unsigned long netByteOrderAddr)
         return true;
     }
     // 100.64.0.0/10 - RFC6598 official CGN address
-    else if ((addr & 0xFFC0) == 0x64400000) {
+    else if ((addr & 0xFFC00000) == 0x64400000) {
         return true;
     }
 
diff --git a/mist/mist.cpp b/mist/mist.cpp
index e4c0896..4474908 100644
--- a/mist/mist.cpp
+++ b/mist/mist.cpp
@@ -555,7 +555,7 @@ bool IsPossibleCGN(PSOCKADDR_IN wanAddr)
         return true;
     }
     // 100.64.0.0/10 - RFC6598 official CGN address
-    else if ((addr & 0xFFC0) == 0x64400000) {
+    else if ((addr & 0xFFC00000) == 0x64400000) {
         return true;
     }