diff --git a/src/main/kotlin/no/item/xp/plugin/DuplicateFieldNameException.kt b/src/main/kotlin/no/item/xp/plugin/DuplicateFieldNameException.kt
new file mode 100644
index 0000000..658e773
--- /dev/null
+++ b/src/main/kotlin/no/item/xp/plugin/DuplicateFieldNameException.kt
@@ -0,0 +1,25 @@
+package no.item.xp.plugin
+
+import org.gradle.api.GradleException
+
+class DuplicateFieldNameException(
+  val fieldNames: List<String>,
+  val source: String? = null,
+) : GradleException(createMessage(fieldNames, source)) {
+  /**
+   * Adds the file the duplicates was found in, unless it has already been added by a more specific caller
+   */
+  fun withSource(source: String): DuplicateFieldNameException =
+    if (this.source == null) DuplicateFieldNameException(fieldNames, source) else this
+}
+
+private fun createMessage(
+  fieldNames: List<String>,
+  source: String?,
+): String {
+  val label = if (fieldNames.size == 1) "Duplicate field name" else "Duplicate field names"
+  val names = fieldNames.joinToString(", ") { "\"$it\"" }
+  val location = source?.let { " in \"$it\"" } ?: ""
+
+  return "$label $names$location. A field name can only be used once in the same object."
+}
diff --git a/src/main/kotlin/no/item/xp/plugin/GenerateCodeTask.kt b/src/main/kotlin/no/item/xp/plugin/GenerateCodeTask.kt
index 1c922b8..a49f244 100644
--- a/src/main/kotlin/no/item/xp/plugin/GenerateCodeTask.kt
+++ b/src/main/kotlin/no/item/xp/plugin/GenerateCodeTask.kt
@@ -122,7 +122,11 @@ open class GenerateCodeTask
             ObjectTypeModel(Paths.get(fileInJar.entry.name).fileName.nameWithoutExtension, emptyList()).right()
           },
           {
-            parseObjectTypeModel(it, Paths.get(fileInJar.entry.name).fileName.nameWithoutExtension, mixins)
+            try {
+              parseObjectTypeModel(it, Paths.get(fileInJar.entry.name).fileName.nameWithoutExtension, mixins)
+            } catch (e: DuplicateFieldNameException) {
+              throw e.withSource(fileInJar.entry.name)
+            }
           },
         ).fold(
           { left ->
diff --git a/src/main/kotlin/no/item/xp/plugin/GenerateTypeScriptWorkAction.kt b/src/main/kotlin/no/item/xp/plugin/GenerateTypeScriptWorkAction.kt
index d309515..e1666ca 100644
--- a/src/main/kotlin/no/item/xp/plugin/GenerateTypeScriptWorkAction.kt
+++ b/src/main/kotlin/no/item/xp/plugin/GenerateTypeScriptWorkAction.kt
@@ -71,6 +71,8 @@ abstract class GenerateTypeScriptWorkAction : WorkAction<CodegenWorkParameters>
             logger.lifecycle("Updated file: ${Path.of(targetFile.absoluteFile.toURI()).toUri()}")
           },
         )
+    } catch (e: DuplicateFieldNameException) {
+      throw e.withSource(simpleFilePath(parameters.getXmlFile().get().asFile))
     } catch (e: Exception) {
       logger.error("Can't parse file", e)
     }
diff --git a/src/main/kotlin/no/item/xp/plugin/parser/ParseInterfaceModel.kt b/src/main/kotlin/no/item/xp/plugin/parser/ParseInterfaceModel.kt
index 1cb191f..1dd91a7 100644
--- a/src/main/kotlin/no/item/xp/plugin/parser/ParseInterfaceModel.kt
+++ b/src/main/kotlin/no/item/xp/plugin/parser/ParseInterfaceModel.kt
@@ -1,6 +1,7 @@
 package no.item.xp.plugin.parser
 
 import arrow.core.Either
+import no.item.xp.plugin.DuplicateFieldNameException
 import no.item.xp.plugin.extensions.getChildNodesAtXPath
 import no.item.xp.plugin.extensions.getChildNodesAtXPathAsEither
 import no.item.xp.plugin.extensions.getNodeAttribute
@@ -37,17 +38,33 @@ fun parseInputTypeList(
   nodes: Collection<Node>,
   mixins: List<ObjectTypeModel>,
 ): List<ObjectTypeModelField> {
-  return nodes
-    .flatMap { node ->
-      when (node.nodeName) {
-        "input" -> listOfNotNull(parseInput(node))
-        "option-set" -> listOfNotNull(parseOptionSet(node, mixins))
-        "item-set" -> listOfNotNull(parseItemSet(node, mixins))
-        "field-set" -> parseFieldSet(node, mixins)
-        "mixin" -> findMixinFields(mixins, node)
-        else -> emptyList()
+  val fields =
+    nodes
+      .flatMap { node ->
+        when (node.nodeName) {
+          "input" -> listOfNotNull(parseInput(node))
+          "option-set" -> listOfNotNull(parseOptionSet(node, mixins))
+          "item-set" -> listOfNotNull(parseItemSet(node, mixins))
+          "field-set" -> parseFieldSet(node, mixins)
+          "mixin" -> findMixinFields(mixins, node)
+          else -> emptyList()
+        }
       }
-    }
+
+  // Fields from mixins and field-sets are added to the same object, so their names can collide
+  val duplicateFieldNames =
+    fields
+      .groupingBy { it.name }
+      .eachCount()
+      .filterValues { it > 1 }
+      .keys
+      .toList()
+
+  if (duplicateFieldNames.isNotEmpty()) {
+    throw DuplicateFieldNameException(duplicateFieldNames)
+  }
+
+  return fields
 }
 
 private fun findMixinFields(
diff --git a/src/main/kotlin/no/item/xp/plugin/parser/ParseMixin.kt b/src/main/kotlin/no/item/xp/plugin/parser/ParseMixin.kt
index eb2237a..dbd13b9 100644
--- a/src/main/kotlin/no/item/xp/plugin/parser/ParseMixin.kt
+++ b/src/main/kotlin/no/item/xp/plugin/parser/ParseMixin.kt
@@ -3,6 +3,7 @@ package no.item.xp.plugin.parser
 import arrow.core.Either
 import arrow.core.flatMap
 import no.item.xp.plugin.CyclicDependenciesException
+import no.item.xp.plugin.DuplicateFieldNameException
 import no.item.xp.plugin.extensions.getChildNodesAtXPath
 import no.item.xp.plugin.extensions.getFormNode
 import no.item.xp.plugin.models.MixinDependencyModel
@@ -82,7 +83,11 @@ private fun walkMixinGraph(
         interfaceModel
       }
 
-  return parseObjectTypeModel(mixin.node, mixin.name, dependentOnMixins).getOrNull()
+  try {
+    return parseObjectTypeModel(mixin.node, mixin.name, dependentOnMixins).getOrNull()
+  } catch (e: DuplicateFieldNameException) {
+    throw e.withSource("site/mixins/${mixin.name}/${mixin.name}.xml")
+  }
 }
 
 fun parseMixinDependencyModel(
diff --git a/src/test/kotlin/no/item/xp/plugin/parser/ParseDuplicateFieldNameTest.kt b/src/test/kotlin/no/item/xp/plugin/parser/ParseDuplicateFieldNameTest.kt
new file mode 100644
index 0000000..c84fb1c
--- /dev/null
+++ b/src/test/kotlin/no/item/xp/plugin/parser/ParseDuplicateFieldNameTest.kt
@@ -0,0 +1,129 @@
+package no.item.xp.plugin.parser
+
+import no.item.xp.plugin.DuplicateFieldNameException
+import no.item.xp.plugin.extensions.getChildNodeAtXPath
+import no.item.xp.plugin.models.ObjectTypeModel
+import no.item.xp.plugin.models.StringField
+import no.item.xp.plugin.stringToXMLDocument
+import org.junit.jupiter.api.Test
+import org.junit.jupiter.api.TestInstance
+import kotlin.test.assertEquals
+import kotlin.test.assertFailsWith
+
+@TestInstance(TestInstance.Lifecycle.PER_CLASS)
+class ParseDuplicateFieldNameTest {
+  private val mixins = listOf(ObjectTypeModel("intro", listOf(StringField("intro", "Intro", true, false))))
+
+  private fun parseForm(xml: String) =
+    parseObjectTypeModel(stringToXMLDocument(xml).getChildNodeAtXPath("content-type/form")!!, "article", mixins)
+
+  @Test
+  fun `fail if mixin contains field with same name`() {
+    // language=XML
+    val xml =
+      """
+      <content-type>
+        <form>
+          <input name="intro" type="TextLine">
+            <label>Intro</label>
+          </input>
+          <mixin name="intro"/>
+        </form>
+      </content-type>
+      """
+
+    val exception = assertFailsWith<DuplicateFieldNameException> { parseForm(xml) }
+
+    assertEquals(listOf("intro"), exception.fieldNames)
+  }
+
+  @Test
+  fun `fail if field-set contains field with same name`() {
+    // language=XML
+    val xml =
+      """
+      <content-type>
+        <form>
+          <item-set name="block">
+            <items>
+              <input name="title" type="TextLine"/>
+              <field-set>
+                <items>
+                  <input name="title" type="TextArea"/>
+                </items>
+              </field-set>
+            </items>
+          </item-set>
+        </form>
+      </content-type>
+      """
+
+    val exception = assertFailsWith<DuplicateFieldNameException> { parseForm(xml) }
+
+    assertEquals(listOf("title"), exception.fieldNames)
+  }
+
+  @Test
+  fun `allow same field name in different objects`() {
+    // language=XML
+    val xml =
+      """
+      <content-type>
+        <form>
+          <input name="title" type="TextLine"/>
+          <item-set name="block">
+            <items>
+              <input name="title" type="TextLine"/>
+            </items>
+          </item-set>
+          <option-set name="link">
+            <options minimum="1" maximum="1">
+              <option name="internal">
+                <items>
+                  <input name="title" type="TextLine"/>
+                </items>
+              </option>
+            </options>
+          </option-set>
+        </form>
+      </content-type>
+      """
+
+    assertEquals(3, parseForm(xml).getOrNull()?.fields?.size)
+  }
+
+  @Test
+  fun `fail with name of mixin that contains duplicates`() {
+    // language=XML
+    val xml =
+      """
+      <mixin>
+        <form>
+          <input name="intro" type="TextLine"/>
+          <mixin name="bb"/>
+        </form>
+      </mixin>
+      """
+
+    // language=XML
+    val xml2 =
+      """
+      <mixin>
+        <form>
+          <input name="intro" type="TextArea"/>
+        </form>
+      </mixin>
+      """
+
+    val mixinDependencies =
+      mapOf("aa" to xml, "bb" to xml2)
+        .map { (name, xml) -> parseMixinDependencyModel(stringToXMLDocument(xml).getChildNodeAtXPath("mixin/form")!!, name) }
+
+    val exception = assertFailsWith<DuplicateFieldNameException> { parseMixin(mixinDependencies.first(), mixinDependencies) }
+
+    assertEquals(
+      "Duplicate field name \"intro\" in \"site/mixins/aa/aa.xml\". A field name can only be used once in the same object.",
+      exception.message,
+    )
+  }
+}