diff --git a/src/seeder/dns.cpp b/src/seeder/dns.cpp
--- a/src/seeder/dns.cpp
+++ b/src/seeder/dns.cpp
@@ -78,6 +78,12 @@
         }
         // add dot in output
         if (!init) {
+            // The maximum size of a query name is 255.
+            // The buffer must have room for the '.' and a valid non-'.'
+            // character
+            if (bufused > 253) {
+                return -1;
+            }
             if (bufused == bufsize - 1) {
                 return -2;
             }
@@ -103,7 +109,7 @@
         }
         // copy label
         while (octet) {
-            if (*inpos == inend) {
+            if (*inpos == inend || bufused > 254) {
                 return -1;
             }
             if (bufused == bufsize - 1) {
diff --git a/src/seeder/test/seeder_tests.cpp b/src/seeder/test/seeder_tests.cpp
--- a/src/seeder/test/seeder_tests.cpp
+++ b/src/seeder/test/seeder_tests.cpp
@@ -119,6 +119,9 @@
 
     // Check that an oversized label causes an error
     CheckParseNameError("www." + maxLengthLabel + "a.com", -1);
+
+    // Check that a query name that is too long causes an error
+    CheckParseNameError(maxLengthQName + "a", -1, 2 * maxLengthQName.size());
 }
 
 BOOST_AUTO_TEST_SUITE_END()