diff --git a/src/seeder/dns.cpp b/src/seeder/dns.cpp
--- a/src/seeder/dns.cpp
+++ b/src/seeder/dns.cpp
@@ -81,11 +81,6 @@
         }
         // add dot in output
         if (!init) {
-            // The maximum size of a query name is 255. The buffer must have
-            // room for at least the '.' and a valid non-'.' character
-            if (bufused > 253) {
-                return -1;
-            }
             if (bufused == bufsize - 1) {
                 return -2;
             }
@@ -109,9 +104,15 @@
         if (octet > 63) {
             return -1;
         }
+        // The maximum size of a query name is 255. The buffer must have
+        // room for the null-character at the end of the buffer after writing
+        // the label.
+        if (octet + bufused > 255) {
+            return -1;
+        }
         // copy label
         while (octet) {
-            if (*inpos == inend || bufused > 254) {
+            if (*inpos == inend) {
                 return -1;
             }
             if (bufused == bufsize - 1) {
diff --git a/src/seeder/test/dns_tests.cpp b/src/seeder/test/dns_tests.cpp
--- a/src/seeder/test/dns_tests.cpp
+++ b/src/seeder/test/dns_tests.cpp
@@ -129,9 +129,13 @@
     CheckParseName(maxLengthQName);
 
     // Check that a query name that is too long causes an error
+    std::string overSizedQName = maxLengthQName;
+    // Split the last label into two while adding an extra character to make
+    // sure the function does not error because of an oversized label
+    overSizedQName.insert(overSizedQName.end() - 3, '.');
     // Allocates an extra large buffer to guarantee an error is not caused by
     // the buffer size
-    CheckParseNameError(maxLengthQName + "a", -1, 2 * maxLengthQName.size());
+    CheckParseNameError(overSizedQName, -1, 2 * overSizedQName.size());
 }
 
 BOOST_AUTO_TEST_SUITE_END()