diff --git a/vscode-extensions/commons/commons-yaml/src/main/java/org/springframework/ide/vscode/commons/yaml/reconcile/SchemaBasedYamlASTReconciler.java b/vscode-extensions/commons/commons-yaml/src/main/java/org/springframework/ide/vscode/commons/yaml/reconcile/SchemaBasedYamlASTReconciler.java
index 3a3f17d4a..cb3fdf45c 100644
--- a/vscode-extensions/commons/commons-yaml/src/main/java/org/springframework/ide/vscode/commons/yaml/reconcile/SchemaBasedYamlASTReconciler.java
+++ b/vscode-extensions/commons/commons-yaml/src/main/java/org/springframework/ide/vscode/commons/yaml/reconcile/SchemaBasedYamlASTReconciler.java
@@ -1,8 +1,12 @@
 package org.springframework.ide.vscode.commons.yaml.reconcile;
 
+import static org.springframework.ide.vscode.commons.yaml.ast.NodeUtil.asScalar;
+
 import java.util.ArrayList;
+import java.util.HashSet;
 import java.util.List;
 import java.util.Map;
+import java.util.Set;
 
 import org.springframework.ide.vscode.commons.languageserver.reconcile.IProblemCollector;
 import org.springframework.ide.vscode.commons.util.ExceptionUtil;
@@ -51,6 +55,7 @@ public class SchemaBasedYamlASTReconciler implements YamlASTReconciler {
 			switch (node.getNodeId()) {
 			case mapping:
 				MappingNode map = (MappingNode) node;
+				checkForDuplicateKeys(map);
 				if (typeUtil.isMap(type)) {
 					for (NodeTuple entry : map.getValue()) {
 						reconcile(doc, entry.getKeyNode(), typeUtil.getKeyType(type));
@@ -108,6 +113,28 @@ public class SchemaBasedYamlASTReconciler implements YamlASTReconciler {
 		}
 	}
 
+	private void checkForDuplicateKeys(MappingNode node) {
+		Set<String> duplicateKeys = new HashSet<>();
+		Set<String> seenKeys = new HashSet<>();
+		for (NodeTuple entry : node.getValue()) {
+			String key = asScalar(entry.getKeyNode());
+			if (key!=null) {
+				if (!seenKeys.add(key)) {
+					duplicateKeys.add(key);
+				}
+			}
+		}
+		if (!duplicateKeys.isEmpty()) {
+			for (NodeTuple entry : node.getValue()) {
+				Node keyNode = entry.getKeyNode();
+				String key = asScalar(keyNode);
+				if (key!=null && duplicateKeys.contains(key)) {
+					problem(keyNode, "Duplicate key '"+key+"'");
+				}
+			}
+		}
+	}
+
 	private void valueParseError(YType type, Node node, String parseErrorMsg) {
 		if (!StringUtil.hasText(parseErrorMsg)) {
 			parseErrorMsg= "Couldn't parse as '"+describe(type)+"'";
diff --git a/vscode-extensions/vscode-concourse/src/test/java/org/springframework/ide/vscode/concourse/PipelineYamlEditorTest.java b/vscode-extensions/vscode-concourse/src/test/java/org/springframework/ide/vscode/concourse/PipelineYamlEditorTest.java
index 6991e0730..c4a0de784 100644
--- a/vscode-extensions/vscode-concourse/src/test/java/org/springframework/ide/vscode/concourse/PipelineYamlEditorTest.java
+++ b/vscode-extensions/vscode-concourse/src/test/java/org/springframework/ide/vscode/concourse/PipelineYamlEditorTest.java
@@ -439,7 +439,30 @@ public class PipelineYamlEditorTest {
 				, // => 
 				"repo-a<*>", "repo-b<*>"
 		);
-
+	}
+	
+	@Test
+	public void reconcileDuplicateKeys() throws Exception {
+		Editor editor = harness.newEditor(
+				"resources:\n" +
+				"- name: my-repo\n" +
+				"  type: git\n" +
+				"  source:\n" +
+				"    repository: https://github.com/kdvolder/my-repo\n" +
+				"resources:\n" +
+				"- name: your-repo\n" +
+				"  type: git\n" +
+				"  type: git\n" +
+				"  source:\n" +
+				"    repository: https://github.com/kdvolder/forked-repo\n"
+		);
+		
+		editor.assertProblems(
+				"resources|Duplicate key",
+				"resources|Duplicate key",
+				"type|Duplicate key",
+				"type|Duplicate key"
+		);
 	}
 
 	//////////////////////////////////////////////////////////////////////////////