diff --git a/build.gradle b/build.gradle
index b150794f..b5522e38 100644
--- a/build.gradle
+++ b/build.gradle
@@ -15,7 +15,7 @@ dependencies {
     compile group: 'com.google.code.gson', name: 'gson', version: '2.6.2'
     compile group: 'commons-io', name: 'commons-io', version: '2.4'
     compile group: 'org.apache.ant', name: 'ant', version: '1.7.1'
-    compile group: 'com.esotericsoftware.yamlbeans', name: 'yamlbeans', version: '1.09'
+    compile group: 'com.github.sanjusoftware', name: 'yamlbeans', version: '1.11'
     testCompile group: 'junit', name: 'junit', version: '4.11'
     testCompile group: 'org.mockito', name: 'mockito-core', version: '1.10.19'
     testCompile group: 'org.hamcrest', name: 'hamcrest-core', version: '1.3'
diff --git a/src/main/java/cd/go/plugin/config/yaml/YamlFileParser.java b/src/main/java/cd/go/plugin/config/yaml/YamlFileParser.java
index bc91bf4f..dfdbdda9 100644
--- a/src/main/java/cd/go/plugin/config/yaml/YamlFileParser.java
+++ b/src/main/java/cd/go/plugin/config/yaml/YamlFileParser.java
@@ -1,6 +1,7 @@
 package cd.go.plugin.config.yaml;
 
 import cd.go.plugin.config.yaml.transforms.RootTransform;
+import com.esotericsoftware.yamlbeans.YamlConfig;
 import com.esotericsoftware.yamlbeans.YamlReader;
 
 import java.io.*;
@@ -22,10 +23,14 @@ public JsonConfigCollection parseFiles(File baseDir, String[] files) {
             InputStream inputStream = null;
             try {
                 inputStream = new FileInputStream(new File(baseDir, file));
-                YamlReader reader = new YamlReader(new InputStreamReader(inputStream));
+                YamlConfig config = new YamlConfig();
+                config.setAllowDuplicates(false);
+                YamlReader reader = new YamlReader(new InputStreamReader(inputStream), config);
                 Object rootObject = reader.read();
                 JsonConfigCollection filePart = rootTransform.transform(rootObject, file);
                 collection.append(filePart);
+            } catch (YamlReader.YamlReaderException ex) {
+                collection.addError("YAML contains duplicate keys: " + ex.getMessage() , file);
             } catch (FileNotFoundException ex) {
                 collection.addError("File matching Go YAML pattern disappeared", file);
             } catch (IOException ex) {
diff --git a/src/test/java/cd/go/plugin/config/yaml/TestUtils.java b/src/test/java/cd/go/plugin/config/yaml/TestUtils.java
index 9d5b4900..dbfea3f3 100644
--- a/src/test/java/cd/go/plugin/config/yaml/TestUtils.java
+++ b/src/test/java/cd/go/plugin/config/yaml/TestUtils.java
@@ -1,5 +1,6 @@
 package cd.go.plugin.config.yaml;
 
+import com.esotericsoftware.yamlbeans.YamlConfig;
 import com.esotericsoftware.yamlbeans.YamlReader;
 import com.google.gson.JsonElement;
 import com.google.gson.JsonParser;
@@ -17,7 +18,9 @@ public static JsonElement readJsonObject(String path) throws IOException {
     }
 
     public static Object readYamlObject(String path) throws IOException {
-        YamlReader reader = new YamlReader(TestUtils.createReader(path));
+        YamlConfig config = new YamlConfig();
+        config.setAllowDuplicates(false);
+        YamlReader reader = new YamlReader(TestUtils.createReader(path), config);
         return reader.read();
     }
 
diff --git a/src/test/java/cd/go/plugin/config/yaml/YamlConfigPluginIntegrationTest.java b/src/test/java/cd/go/plugin/config/yaml/YamlConfigPluginIntegrationTest.java
index b3e07170..0f2ebbf3 100644
--- a/src/test/java/cd/go/plugin/config/yaml/YamlConfigPluginIntegrationTest.java
+++ b/src/test/java/cd/go/plugin/config/yaml/YamlConfigPluginIntegrationTest.java
@@ -169,6 +169,27 @@ public void shouldRespondSuccessWithErrorMessagesToParseDirectoryRequestWhenSimp
         assertThat(errors.get(0).getAsJsonObject().getAsJsonPrimitive("location").getAsString(), is("simple-invalid.gocd.yaml"));
     }
 
+    @Test
+    public void shouldRespondSuccessWithErrorMessagesToParseDirectoryRequestWhenDuplicateKeysCaseFile() throws UnhandledRequestTypeException, IOException {
+        setupCase("simpleInvalidCase", "duplicate-materials");
+
+        DefaultGoPluginApiRequest parseDirectoryRequest = new DefaultGoPluginApiRequest("configrepo", "1.0", "parse-directory");
+        String requestBody = "{\n" +
+                "    \"directory\":\"simpleInvalidCase\",\n" +
+                "    \"configurations\":[]\n" +
+                "}";
+        parseDirectoryRequest.setRequestBody(requestBody);
+
+        GoPluginApiResponse response = plugin.handle(parseDirectoryRequest);
+        assertThat(response.responseCode(), is(DefaultGoPluginApiResponse.SUCCESS_RESPONSE_CODE));
+        JsonObject responseJsonObject = getJsonObjectFromResponse(response);
+        JsonArray errors = (JsonArray) responseJsonObject.get("errors");
+        JsonArray pipelines = responseJsonObject.get("pipelines").getAsJsonArray();
+        assertThat(pipelines.size(), is(0));
+        assertThat(errors.get(0).getAsJsonObject().getAsJsonPrimitive("message").getAsString(), is("YAML contains duplicate keys: Line 9, column 20: Duplicate key found 'upstream'"));
+        assertThat(errors.get(0).getAsJsonObject().getAsJsonPrimitive("location").getAsString(), is("duplicate-materials.gocd.yaml"));
+    }
+
     private void setupCase(String folder, String caseName) throws IOException {
         File caseFolder = new File(folder);
         FileUtils.deleteDirectory(caseFolder);
diff --git a/src/test/java/cd/go/plugin/config/yaml/transforms/RootTransformTest.java b/src/test/java/cd/go/plugin/config/yaml/transforms/RootTransformTest.java
index edcfeb88..63392f33 100644
--- a/src/test/java/cd/go/plugin/config/yaml/transforms/RootTransformTest.java
+++ b/src/test/java/cd/go/plugin/config/yaml/transforms/RootTransformTest.java
@@ -1,6 +1,8 @@
 package cd.go.plugin.config.yaml.transforms;
 
 import cd.go.plugin.config.yaml.JsonConfigCollection;
+import cd.go.plugin.config.yaml.YamlConfigException;
+import com.esotericsoftware.yamlbeans.YamlReader;
 import org.junit.Before;
 import org.junit.Test;
 
@@ -9,6 +11,7 @@
 import static cd.go.plugin.config.yaml.TestUtils.readYamlObject;
 import static org.hamcrest.core.Is.is;
 import static org.junit.Assert.assertThat;
+import static org.junit.Assert.fail;
 import static org.mockito.Mockito.mock;
 
 public class RootTransformTest {
@@ -40,6 +43,12 @@ public void shouldTransformRootWhen2PipelinesAnd2Environments() throws IOExcepti
         assertThat(collection.getJsonObject().get("pipelines").getAsJsonArray().size(), is(2));
     }
 
+    @Test(expected = YamlReader.YamlReaderException.class)
+    public void shouldNotTransformRootWhenYAMLHasDuplicateKeys() throws IOException {
+        readRootYaml("duplicate.materials.pipe");
+        fail("should have thrown duplicate keys error");
+    }
+
     private JsonConfigCollection readRootYaml(String caseFile) throws IOException {
         return rootTransform.transform(readYamlObject("parts/roots/" + caseFile + ".yaml"), "test code");
     }
diff --git a/src/test/resources/examples/duplicate-materials.gocd.yaml b/src/test/resources/examples/duplicate-materials.gocd.yaml
new file mode 100644
index 00000000..659ae073
--- /dev/null
+++ b/src/test/resources/examples/duplicate-materials.gocd.yaml
@@ -0,0 +1,10 @@
+pipelines:
+  pipe1:
+    group: group
+    materials:
+      upstream:
+        pipeline: upstream-pipeline-1
+        stage: test1
+      upstream:
+        pipeline: upstream-pipeline-2
+        stage: test2
\ No newline at end of file
diff --git a/src/test/resources/parts/roots/duplicate.materials.pipe.yaml b/src/test/resources/parts/roots/duplicate.materials.pipe.yaml
new file mode 100644
index 00000000..659ae073
--- /dev/null
+++ b/src/test/resources/parts/roots/duplicate.materials.pipe.yaml
@@ -0,0 +1,10 @@
+pipelines:
+  pipe1:
+    group: group
+    materials:
+      upstream:
+        pipeline: upstream-pipeline-1
+        stage: test1
+      upstream:
+        pipeline: upstream-pipeline-2
+        stage: test2
\ No newline at end of file