diff --git a/src/main/java/org/raml/parser/builder/DefaultTupleBuilder.java b/src/main/java/org/raml/parser/builder/DefaultTupleBuilder.java
index 7cb523ee..22b903ee 100644
--- a/src/main/java/org/raml/parser/builder/DefaultTupleBuilder.java
+++ b/src/main/java/org/raml/parser/builder/DefaultTupleBuilder.java
@@ -65,7 +65,7 @@ public NodeBuilder getBuilderForTuple(NodeTuple tuple)
                 return tupleBuilder;
             }
         }
-        throw new RuntimeException("Builder not found for " + tuple);
+        return null;
     }
 
     protected Map<String, TupleBuilder<?, ?>> getBuilders()
diff --git a/src/main/java/org/raml/parser/visitor/YamlDocumentBuilder.java b/src/main/java/org/raml/parser/visitor/YamlDocumentBuilder.java
index ecb9d601..860ac0c1 100644
--- a/src/main/java/org/raml/parser/visitor/YamlDocumentBuilder.java
+++ b/src/main/java/org/raml/parser/visitor/YamlDocumentBuilder.java
@@ -270,6 +270,10 @@ public boolean onTupleStart(NodeTuple nodeTuple)
         if (currentBuilder != null)
         {
             NodeBuilder<?> builder = currentBuilder.getBuilderForTuple(nodeTuple);
+            if (builder == null)
+            {
+                return false;
+            }
             builderContext.push(builder);
         }
         else
diff --git a/src/main/java/org/raml/parser/visitor/YamlDocumentSuggester.java b/src/main/java/org/raml/parser/visitor/YamlDocumentSuggester.java
index 5290dc31..1a393efd 100644
--- a/src/main/java/org/raml/parser/visitor/YamlDocumentSuggester.java
+++ b/src/main/java/org/raml/parser/visitor/YamlDocumentSuggester.java
@@ -307,7 +307,11 @@ public boolean onTupleStart(NodeTuple nodeTuple)
     {
         try
         {
-            builder.onTupleStart(nodeTuple);
+            boolean found = builder.onTupleStart(nodeTuple);
+            if (!found)
+            {
+                return false;
+            }
             MappingNode mapping = nodeTuple.getValueNode().getNodeId() == NodeId.mapping ? (MappingNode) nodeTuple.getValueNode() : null;
             pushNode(nodeTuple.getKeyNode(), mapping);
         }
diff --git a/src/test/java/org/raml/validation/ValidationTestCase.java b/src/test/java/org/raml/validation/ValidationTestCase.java
index 2800465c..3572ffa3 100644
--- a/src/test/java/org/raml/validation/ValidationTestCase.java
+++ b/src/test/java/org/raml/validation/ValidationTestCase.java
@@ -16,6 +16,7 @@
 package org.raml.validation;
 
 import static org.hamcrest.CoreMatchers.is;
+import static org.hamcrest.CoreMatchers.notNullValue;
 import static org.hamcrest.CoreMatchers.nullValue;
 import static org.junit.Assert.assertThat;
 import static org.junit.matchers.JUnitMatchers.containsString;
@@ -28,11 +29,13 @@
 
 import org.junit.Ignore;
 import org.junit.Test;
+import org.raml.model.ActionType;
 import org.raml.model.Raml;
 import org.raml.parser.builder.AbstractRamlTestCase;
 import org.raml.parser.rule.ValidationResult;
 import org.raml.parser.tagresolver.ContextPath;
 import org.raml.parser.visitor.IncludeInfo;
+import org.raml.parser.visitor.RamlDocumentBuilder;
 
 public class ValidationTestCase extends AbstractRamlTestCase
 {
@@ -222,6 +225,21 @@ public void circularInclude()
         assertThat(includeInfo.getLine() + 1, is(3));
     }
 
+    @Test
+    public void unknownKey()
+    {
+        String resource = "org/raml/validation/unknown-key.yaml";
+        
+        // validation reports the unknown key...
+        List<ValidationResult> validationResults = validateRaml(resource);
+        assertThat(validationResults.size(), is(1));
+        assertThat(validationResults.get(0).getMessage(), is("Unknown key: unknown"));
+        
+        // ... but the parser doesn't choke on it
+        Raml validContent = new RamlDocumentBuilder().build(resource);
+        assertThat(validContent.getResource("/partiallyInvalid").getAction(ActionType.POST), is(notNullValue()));
+    }
+
     @Test
     public void badMediaTypeName()
     {
diff --git a/src/test/resources/org/raml/validation/unknown-key.yaml b/src/test/resources/org/raml/validation/unknown-key.yaml
new file mode 100644
index 00000000..a4499700
--- /dev/null
+++ b/src/test/resources/org/raml/validation/unknown-key.yaml
@@ -0,0 +1,7 @@
+#%RAML 0.8
+title: unknown key
+/partiallyInvalid:
+    post:
+        unknown:
+        body:
+            application/json: