diff --git a/src/lib/dns/cpp/rrparamregistry.cc b/src/lib/dns/cpp/rrparamregistry.cc
index b267cd192c..6a9bcab6fa 100644
--- a/src/lib/dns/cpp/rrparamregistry.cc
+++ b/src/lib/dns/cpp/rrparamregistry.cc
@@ -14,6 +14,7 @@
 
 // $Id$
 
+#include <cassert>
 #include <algorithm>
 #include <cctype>
 #include <functional>
@@ -213,9 +214,7 @@ bool CICharEqual(char c1, char c2)
 bool
 caseStringEqual(const string& s1, const string& s2, size_t n)
 {
-    if (s1.size() < n || s2.size() < n) {
-        return (false);
-    }
+    assert(s1.size() >= n && s2.size() >= n);
 
     return (mismatch(s1.begin(), s1.begin() + n, s2.begin(), CICharEqual).first
             == s1.begin() + n);
diff --git a/src/lib/dns/cpp/rrparamregistry_unittest.cc b/src/lib/dns/cpp/rrparamregistry_unittest.cc
index efb16a05a1..a5d7d99017 100644
--- a/src/lib/dns/cpp/rrparamregistry_unittest.cc
+++ b/src/lib/dns/cpp/rrparamregistry_unittest.cc
@@ -62,10 +62,17 @@ TEST_F(RRParamRegistryTest, addRemove)
     EXPECT_EQ(65533, RRClass("TESTCLASS").getCode());
     EXPECT_EQ(65534, RRType("TESTTYPE").getCode());
 
+    // the first removal attempt should succeed
+    EXPECT_TRUE(RRParamRegistry::getRegistry().removeType(65534));
+    // then toText() should treat it as an "unknown" 
+    EXPECT_EQ(test_type_unknown_str, RRType(test_type_code).toText());
+    // attempt of removing non-existent mapping should result in 'false'
+    EXPECT_FALSE(RRParamRegistry::getRegistry().removeType(65534));
+
+    // same set of tests for RR class.
     EXPECT_TRUE(RRParamRegistry::getRegistry().removeClass(65533));
     EXPECT_EQ(test_class_unknown_str, RRClass(test_class_code).toText());
-    EXPECT_TRUE(RRParamRegistry::getRegistry().removeType(65534));
-    EXPECT_EQ(test_type_unknown_str, RRType(test_type_code).toText());
+    EXPECT_FALSE(RRParamRegistry::getRegistry().removeClass(65533));
 }
 
 TEST_F(RRParamRegistryTest, addError)