diff --git a/jr-stree/src/main/java/com/fasterxml/jackson/jr/stree/JacksonJrsTreeCodec.java b/jr-stree/src/main/java/com/fasterxml/jackson/jr/stree/JacksonJrsTreeCodec.java
index 94550cf5..6e14afe5 100644
--- a/jr-stree/src/main/java/com/fasterxml/jackson/jr/stree/JacksonJrsTreeCodec.java
+++ b/jr-stree/src/main/java/com/fasterxml/jackson/jr/stree/JacksonJrsTreeCodec.java
@@ -64,11 +64,11 @@ private JrsValue nodeFrom(JsonParser p) throws IOException
             Map<String, JrsValue> values = _map();
             while (p.nextToken() != JsonToken.END_OBJECT) {
                 final String currentName = p.currentName();
-                if (duplicateCheck(values, currentName)) {
+                p.nextToken();
+                JrsValue prev = values.put(currentName, nodeFrom(p));
+                if (_failOnDuplicateKeys && (prev != null)) {
                     throw new JSONObjectException("Duplicate key (key '" + currentName + "')");
                 }
-                p.nextToken();
-                values.put(currentName, nodeFrom(p));
             }
             return new JrsObject(values);
         }
@@ -84,10 +84,6 @@ private JrsValue nodeFrom(JsonParser p) throws IOException
         throw new UnsupportedOperationException("Unsupported token id " + tokenId + " (" + p.currentToken() + ")");
     }
 
-    private boolean duplicateCheck(Map<String, JrsValue> values, String currentName) {
-        return _failOnDuplicateKeys && values.containsKey(currentName);
-    }
-
     @Override
     public void writeTree(JsonGenerator g, TreeNode treeNode) throws IOException {
         if (treeNode == null) {
diff --git a/jr-stree/src/test/java/com/fasterxml/jackson/jr/stree/DupFieldNameInTree51Test.java b/jr-stree/src/test/java/com/fasterxml/jackson/jr/stree/DupFieldNameInTree51Test.java
index 42097a8a..0869bfdf 100644
--- a/jr-stree/src/test/java/com/fasterxml/jackson/jr/stree/DupFieldNameInTree51Test.java
+++ b/jr-stree/src/test/java/com/fasterxml/jackson/jr/stree/DupFieldNameInTree51Test.java
@@ -7,37 +7,32 @@
  * Tests for reading content using {@link JSON} with proper
  * codec registration
  */
-public class DupFieldNameInTree51Test extends JacksonJrTreeTestBase {
-
+public class DupFieldNameInTree51Test extends JacksonJrTreeTestBase
+{
+    private final JSON NO_DUPS_JSON = JSON.builder()
+            .enable(JSON.Feature.FAIL_ON_DUPLICATE_MAP_KEYS)
+            .register(new JrSimpleTreeExtension())
+            .build();
+
+    private final JSON DUPS_OK_JSON = JSON.builder()
+            .disable(JSON.Feature.FAIL_ON_DUPLICATE_MAP_KEYS)
+            .register(new JrSimpleTreeExtension())
+            .build();
+    
     // [jackson-jr#51]: test dup keys for trees too
-    public void testFailOnDupMapKeys() throws Exception {
-        JSON j = JSON.builder()
-                .enable(JSON.Feature.FAIL_ON_DUPLICATE_MAP_KEYS)
-                .build();
-
-        final JSON treeJSON = jsonWithTreeCodec(j);
-
-        assertTrue(j.isEnabled(JSON.Feature.FAIL_ON_DUPLICATE_MAP_KEYS));
+    public void testFailOnDupMapKeys() throws Exception
+    {
+        assertTrue(NO_DUPS_JSON.isEnabled(JSON.Feature.FAIL_ON_DUPLICATE_MAP_KEYS));
         final String json = "{\"a\":1,\"b\":2,\"b\":3,\"c\":4}";
         try {
-            /*TreeNode node =*/ treeJSON.treeFrom(json);
+            /*TreeNode node =*/ NO_DUPS_JSON.treeFrom(json);
+            fail("Should not pass");
         } catch (JSONObjectException e) {
             verifyException(e, "Duplicate key");
         }
-    }
-
-    public void testFailOnDupMapKeys2() throws Exception {
-        //missing flag - Enabled by default!
-        JSON j = JSON.builder().build();
-
-        final JSON treeJSON = jsonWithTreeCodec(j);
 
-        assertTrue(j.isEnabled(JSON.Feature.FAIL_ON_DUPLICATE_MAP_KEYS));
-        final String json = "{\"a\":1,\"b\":2,\"b\":3,\"c\":4}";
-        try {
-            /*TreeNode node =*/ treeJSON.treeFrom(json);
-        } catch (JSONObjectException e) {
-            verifyException(e, "Duplicate key");
-        }
+        assertFalse(DUPS_OK_JSON.isEnabled(JSON.Feature.FAIL_ON_DUPLICATE_MAP_KEYS));
+        // But should pass fine without setting
+        assertNotNull(DUPS_OK_JSON.treeFrom(json));
     }
 }
diff --git a/jr-stree/src/test/java/com/fasterxml/jackson/jr/stree/JacksonJrTreeTestBase.java b/jr-stree/src/test/java/com/fasterxml/jackson/jr/stree/JacksonJrTreeTestBase.java
index 9f00883e..1422c079 100644
--- a/jr-stree/src/test/java/com/fasterxml/jackson/jr/stree/JacksonJrTreeTestBase.java
+++ b/jr-stree/src/test/java/com/fasterxml/jackson/jr/stree/JacksonJrTreeTestBase.java
@@ -44,14 +44,6 @@ protected String a2q(String json) {
         return json.replace("'", "\"");
     }
 
-    protected JSON jsonWithTreeCodec(JSON config) {
-        return JSON.builder()
-                // 13-Feb-2020, tatu: There are 2 different ways actually..
-//            .treeCodec(new JacksonJrsTreeCodec())
-                .register(new JrSimpleTreeExtension())
-            .build();
-    }
-
     protected JSON jsonWithTreeCodec() {
         return JSON.builder()
                 // 13-Feb-2020, tatu: There are 2 different ways actually..