diff --git a/src/root.js b/src/root.js
index 13be39d89..2e57b3486 100644
--- a/src/root.js
+++ b/src/root.js
@@ -260,7 +260,7 @@ var exposeRe = /^[A-Z]/;
 function tryHandleExtension(root, field) {
     var extendedType = field.parent.lookup(field.extend);
     if (extendedType) {
-        var sisterField = new Field(field.fullName, field.id, field.type, field.rule, undefined, field.options);
+        var sisterField = new Field(field.name, field.id, field.type, field.rule, undefined, field.options);
         sisterField.declaringField = field;
         field.extensionField = sisterField;
         extendedType.add(sisterField);
diff --git a/tests/api_root-deferred.js b/tests/api_root-deferred.js
index 577e7b5dc..7010f0eb2 100644
--- a/tests/api_root-deferred.js
+++ b/tests/api_root-deferred.js
@@ -17,15 +17,15 @@ tape.test("extension fields", function(test) {
 
     var extendedType = new Type("ExtendedType");
     ns.add(extendedType);
-    var extensionField = extendedType.get(declaringField.fullName);
+    var extensionField = extendedType.get(declaringField.name);
     test.equal(extensionField, declaringField.extensionField, "should become available once their extended type is known");
 
     type.remove(declaringField);
-    extensionField = extendedType.get(declaringField.fullName);
+    extensionField = extendedType.get(declaringField.name);
     test.equal(extensionField, null, "should become unavailable when their declaring field is removed");
 
     type.add(declaringField);
-    extensionField = extendedType.get(declaringField.fullName);
+    extensionField = extendedType.get(declaringField.name);
     test.equal(extensionField, declaringField.extensionField, "should become instantly available if their extended type is knwon");
 
     ns.remove(extendedType);
diff --git a/tests/comp_extend.js b/tests/comp_extend.js
index 4d9d19556..95fd2131a 100644
--- a/tests/comp_extend.js
+++ b/tests/comp_extend.js
@@ -14,14 +14,28 @@ message A {\
         message Two {\
             extend B.One {\
                 C.Two two = 1000;\
+                string extended = 1001;\
             }\
         }\
     }\
 }";
 
 tape.test("extensions", function(test) {
-    var root = protobuf.parse(proto).root;
-    root.resolveAll();
-    test.pass("should parse and resolve without errors");
-    test.end();
+
+    test.test(" - parsing", function(test) {
+        var root = protobuf.parse(proto).root;
+        root.resolveAll();
+        test.pass("should parse and resolve without errors");
+        test.end();
+    });
+
+    test.test(" - encoding", function(test) {
+        var root = protobuf.parse(proto).root;
+        root.resolveAll();
+        var one = root.lookupType("A.B.One");
+        var original = {extended: "test"};
+        var cycled = one.decode(one.encode(original).finish());
+        test.deepEqual(cycled, original, "should write and read back");
+        test.end();
+    });
 });