diff --git a/test/test_util.cpp b/test/test_util.cpp
index 7742ca7..98d1c42 100644
--- a/test/test_util.cpp
+++ b/test/test_util.cpp
@@ -164,10 +164,46 @@
     prefix = toCidr(AF_INET6, mask);
     EXPECT_EQ(prefix, 38);
 
-    // Invalid Mask
+    mask = "ffff:0:0:0:0:0:0:0";
+    prefix = toCidr(AF_INET6, mask);
+    EXPECT_EQ(prefix, 16);
+
+    mask = "ffff:ffff:ffff:ffff:ffff:ffff:ffff:ffff";
+    prefix = toCidr(AF_INET6, mask);
+    EXPECT_EQ(prefix, 128);
+
+    mask = "ffff:ffff:ffff:ffff:ffff:ffff:ffff:fffc";
+    prefix = toCidr(AF_INET6, mask);
+    EXPECT_EQ(prefix, 126);
+
+    // Invalid Masks
     mask = "ffff:0fff::";
     prefix = toCidr(AF_INET6, mask);
     EXPECT_EQ(prefix, 0);
+
+    mask = "ffff:fgff::";
+    prefix = toCidr(AF_INET6, mask);
+    EXPECT_EQ(prefix, 0);
+
+    mask = "ffff:0:0:6:0:0:0:0";
+    prefix = toCidr(AF_INET6, mask);
+    EXPECT_EQ(prefix, 0);
+
+    mask = "::";
+    prefix = toCidr(AF_INET6, mask);
+    EXPECT_EQ(prefix, 0);
+
+    mask = ":";
+    prefix = toCidr(AF_INET6, mask);
+    EXPECT_EQ(prefix, 0);
+
+    mask = "abcd:efgh:ijkl:mnop:pqrs:tuvw:xyz:abcd";
+    prefix = toCidr(AF_INET6, mask);
+    EXPECT_EQ(prefix, 0);
+
+    mask = "ffff:0:0:0:0:0:0";
+    prefix = toCidr(AF_INET6, mask);
+    EXPECT_EQ(prefix, 0);
 }
 
 TEST_F(TestUtil, isLinkLocaladdress)