diff --git a/lint-checks/src/main/java/androidx/build/lint/aidl/AidlDefinitionDetector.kt b/lint-checks/src/main/java/androidx/build/lint/aidl/AidlDefinitionDetector.kt
index b1e086f..d219896 100644
--- a/lint-checks/src/main/java/androidx/build/lint/aidl/AidlDefinitionDetector.kt
+++ b/lint-checks/src/main/java/androidx/build/lint/aidl/AidlDefinitionDetector.kt
@@ -31,33 +31,51 @@
 import com.android.tools.lint.detector.api.Scope
 import com.intellij.core.CoreFileTypeRegistry
 import com.intellij.lang.LanguageParserDefinitions
+import com.intellij.openapi.fileTypes.LanguageFileType
 import com.intellij.openapi.fileTypes.UnknownFileType
 import com.intellij.openapi.vfs.local.CoreLocalFileSystem
 import com.intellij.psi.PsiManager
 import com.intellij.psi.SingleRootFileViewProvider
 import java.io.File
+import java.lang.reflect.Method
 
 /**
  * Abstract class for detectors running against AIDL definitions (e.g. .aidl files).
  */
 abstract class AidlDefinitionDetector : Detector(), OtherFileScanner {
 
-    override fun getApplicableFiles() = Scope.OTHER_SCOPE
+    private var delegate: Any? = null
+    private var methodRun: Method? = null
 
     override fun beforeCheckEachProject(context: Context) {
-        val aidlFileType = AidlFileType.INSTANCE
+        val detectorClass = this.javaClass
+        var aidlFileType: LanguageFileType = AidlFileType.INSTANCE
+        var useMethodRun: Method? = null
+        var useDelegate: Any? = null
 
-        // We only need to register the language parser once per daemon process...
+        // Register the parser, if it hasn't already been registered by another instance.
         LanguageParserDefinitions.INSTANCE.apply {
             synchronized(this) {
-                val existingParsers = forLanguage(aidlFileType.language)
-                if (existingParsers == null) {
+                val existingParser = forLanguage(aidlFileType.language)
+                if (existingParser == null) {
                     addExplicitExtension(aidlFileType.language, AidlParserDefinition())
+                } else {
+                    // An instance of this class already registered the parser, potentially from a
+                    // different ClassLoader. Avoid conflicts (see b/300097739) by delegating to a
+                    // detector instance loaded from the registered parser's ClassLoader.
+                    val classLoader = existingParser.javaClass.classLoader
+                    classLoader.loadClass(detectorClass.name).let {
+                        useDelegate = it.getConstructor().newInstance()
+                        useMethodRun = it.getMethod("runInternal", Context::class.java)
+                    }
+                    classLoader.loadClass(AidlFileType::class.qualifiedName).let {
+                        aidlFileType = it.getField("INSTANCE").get(null) as LanguageFileType
+                    }
                 }
             }
         }
 
-        // ...but we need to register the file type every time we run Gradle.
+        // Register the file type, if it hasn't already ben registered by another instance.
         (CoreFileTypeRegistry.getInstance() as CoreFileTypeRegistry).apply {
             synchronized(this) {
                 val existingFileType = getFileTypeByExtension(aidlFileType.defaultExtension)
@@ -66,9 +84,24 @@
                 }
             }
         }
+
+        delegate = useDelegate
+        methodRun = useMethodRun
     }
 
+    override fun getApplicableFiles() = Scope.OTHER_SCOPE
+
     override fun run(context: Context) {
+        // Call the delegate's run method, if we have one.
+        methodRun?.invoke(delegate, context) ?: runInternal(context)
+    }
+
+    /**
+     * Actual implementation of [run]. This must be Java-visible since it will be called via
+     * reflection from what is _technically_ a different class.
+     */
+    @Suppress("MemberVisibilityCanBePrivate")
+    fun runInternal(context: Context) {
         if (context.file.extension == AidlFileType.DEFAULT_ASSOCIATED_EXTENSION) {
             ioFileToAidlFile(context, context.file)
                 .allAidlDeclarations
@@ -84,6 +117,8 @@
                 visitAidlInterfaceDeclaration(context, aidlDeclaration)
             is AidlParcelableDeclaration ->
                 visitAidlParcelableDeclaration(context, aidlDeclaration)
+            is AidlMethodDeclaration ->
+                visitAidlMethodDeclaration(context, aidlDeclaration)
             is AidlUnionDeclaration -> {
                 listOf(
                     aidlDeclaration.interfaceDeclarationList,
diff --git a/lint-checks/src/test/java/androidx/build/lint/AbstractLintDetectorTest.kt b/lint-checks/src/test/java/androidx/build/lint/AbstractLintDetectorTest.kt
index 0ed4dd8..3cd0e5c 100644
--- a/lint-checks/src/test/java/androidx/build/lint/AbstractLintDetectorTest.kt
+++ b/lint-checks/src/test/java/androidx/build/lint/AbstractLintDetectorTest.kt
@@ -73,6 +73,7 @@
                 *stubs,
                 *files
             )
+            .allowDuplicates()
             .run()
     }
 }