diff --git a/src/main/kotlin/com/autonomousapps/extension/IssueHandler.kt b/src/main/kotlin/com/autonomousapps/extension/IssueHandler.kt
index 19cf63a0d..bcb53c51d 100644
--- a/src/main/kotlin/com/autonomousapps/extension/IssueHandler.kt
+++ b/src/main/kotlin/com/autonomousapps/extension/IssueHandler.kt
@@ -65,6 +65,10 @@ abstract class IssueHandler @Inject constructor(
     return globalDslService.unusedAnnotationProcessorsIssueFor(projectPath)
   }
 
+  internal fun onDuplicateClassWarnings(projectPath: String): List<Provider<Behavior>> {
+    return globalDslService.onDuplicateClassWarnings(projectPath)
+  }
+
   internal fun redundantPluginsIssueFor(projectPath: String): Provider<Behavior> {
     return globalDslService.redundantPluginsIssueFor(projectPath)
   }
diff --git a/src/main/kotlin/com/autonomousapps/extension/ProjectIssueHandler.kt b/src/main/kotlin/com/autonomousapps/extension/ProjectIssueHandler.kt
index c6cb9c4ea..58a0949e8 100644
--- a/src/main/kotlin/com/autonomousapps/extension/ProjectIssueHandler.kt
+++ b/src/main/kotlin/com/autonomousapps/extension/ProjectIssueHandler.kt
@@ -20,7 +20,15 @@ import javax.inject.Inject
  *       ignoreSourceSet(...)
  *
  *       // Specify severity and exclude rules for all types of dependency violations.
- *       onAny { ... }
+ *       onAny {
+ *         severity(<"fail"|"warn"|"ignore">)
+ *
+ *         // using version catalog accessors
+ *         exclude(libs.guava, ...)
+ *
+ *         // using basic string coordinates
+ *         exclude("com.google.guava:guava", ...)
+ *       }
  *
  *       // Specify severity and exclude rules for unused dependencies.
  *       onUnusedDependencies { ... }
@@ -47,8 +55,15 @@ import javax.inject.Inject
  *
  *       // Specify severity and exclude rules for module structure advice.
  *       onModuleStructure {
- *         severity(<'fail'|'warn'|'ignore'>)
- *         exclude('android')
+ *         severity(<"fail"|"warn"|"ignore">)
+ *         exclude("android")
+ *       }
+ *
+ *       onDuplicateClassWarnings {
+ *          severity(<"fail"|"warn"|"ignore">)
+ *
+ *          // Fully-qualified class reference to exclude, slash- or dot-delimited
+ *          exclude("org/jetbrains/annotations/NotNull", "org.jetbrains.annotations.Nullable")
  *       }
  *     }
  *   }
@@ -76,6 +91,7 @@ abstract class ProjectIssueHandler @Inject constructor(
   internal val runtimeOnlyIssue = objects.newInstance<Issue>()
   internal val redundantPluginsIssue = objects.newInstance<Issue>()
   internal val moduleStructureIssue = objects.newInstance<Issue>()
+  internal val duplicateClassWarningsIssue = objects.newInstance<Issue>()
 
   internal val ignoreSourceSets = objects.setProperty<String>()
 
@@ -125,4 +141,8 @@ abstract class ProjectIssueHandler @Inject constructor(
   fun onModuleStructure(action: Action<Issue>) {
     action.execute(moduleStructureIssue)
   }
+
+  fun onDuplicateClassWarnings(action: Action<Issue>) {
+    action.execute(duplicateClassWarningsIssue)
+  }
 }
diff --git a/src/main/kotlin/com/autonomousapps/internal/advice/SeverityHandler.kt b/src/main/kotlin/com/autonomousapps/internal/advice/SeverityHandler.kt
index c7e446867..f2423bbe8 100644
--- a/src/main/kotlin/com/autonomousapps/internal/advice/SeverityHandler.kt
+++ b/src/main/kotlin/com/autonomousapps/internal/advice/SeverityHandler.kt
@@ -2,14 +2,15 @@
 // SPDX-License-Identifier: Apache-2.0
 package com.autonomousapps.internal.advice
 
-import com.autonomousapps.model.PluginAdvice
 import com.autonomousapps.extension.Behavior
 import com.autonomousapps.extension.Fail
 import com.autonomousapps.internal.DependencyScope
 import com.autonomousapps.internal.utils.filterToSet
 import com.autonomousapps.internal.utils.lowercase
 import com.autonomousapps.model.Advice
+import com.autonomousapps.model.DuplicateClass
 import com.autonomousapps.model.ModuleAdvice
+import com.autonomousapps.model.PluginAdvice
 import com.autonomousapps.model.Advice as DependencyAdvice
 
 /** Given the set of all behaviors, determine whether the analysis should fail the build. */
@@ -20,20 +21,33 @@ internal class SeverityHandler(
   private val incorrectConfigurationBehavior: Pair<Behavior, List<Behavior>>,
   private val compileOnlyBehavior: Pair<Behavior, List<Behavior>>,
   private val unusedProcsBehavior: Pair<Behavior, List<Behavior>>,
+  private val duplicateClassWarningsBehavior: Pair<Behavior, List<Behavior>>,
   private val redundantPluginsBehavior: Behavior,
   private val moduleStructureBehavior: Behavior,
 ) {
 
   fun shouldFailDeps(advice: Set<DependencyAdvice>): Boolean {
-    return shouldFailFor(anyBehavior, advice) ||
-      shouldFailFor(unusedDependenciesBehavior, advice.filterToSet { it.isRemove() }) ||
-      shouldFailFor(usedTransitiveDependenciesBehavior, advice.filterToSet { it.isAdd() }) ||
-      shouldFailFor(incorrectConfigurationBehavior, advice.filterToSet { it.isChange() }) ||
-      shouldFailFor(compileOnlyBehavior, advice.filterToSet { it.isCompileOnly() }) ||
-      shouldFailFor(unusedProcsBehavior, advice.filterToSet { it.isProcessor() })
+    return shouldFailForAdvice(anyBehavior, advice) ||
+      shouldFailForAdvice(unusedDependenciesBehavior, advice.filterToSet { it.isRemove() }) ||
+      shouldFailForAdvice(usedTransitiveDependenciesBehavior, advice.filterToSet { it.isAdd() }) ||
+      shouldFailForAdvice(incorrectConfigurationBehavior, advice.filterToSet { it.isChange() }) ||
+      shouldFailForAdvice(compileOnlyBehavior, advice.filterToSet { it.isCompileOnly() }) ||
+      shouldFailForAdvice(unusedProcsBehavior, advice.filterToSet { it.isProcessor() })
+  }
+
+  fun shouldFailPlugins(pluginAdvice: Set<PluginAdvice>): Boolean {
+    return (redundantPluginsBehavior.isFail() || anyBehavior.first.isFail()) && pluginAdvice.isNotEmpty()
+  }
+
+  fun shouldFailModuleStructure(moduleAdvice: Set<ModuleAdvice>): Boolean {
+    return (moduleStructureBehavior.isFail() || anyBehavior.first.isFail()) && ModuleAdvice.isNotEmpty(moduleAdvice)
+  }
+
+  fun shouldFailDuplicateClasses(duplicateClasses: Set<DuplicateClass>): Boolean {
+    return shouldFailForDuplicateClasses(duplicateClassWarningsBehavior, duplicateClasses)
   }
 
-  private fun shouldFailFor(
+  private fun shouldFailForAdvice(
     spec: Pair<Behavior, List<Behavior>>,
     advice: Set<DependencyAdvice>,
   ): Boolean {
@@ -50,7 +64,6 @@ internal class SeverityHandler(
         b.sourceSetName == from || b.sourceSetName == to
       }
 
-
       // Looking for a match between sourceSet-specific behavior and advice.
       var shouldFail = false
       behaviors.forEach { b ->
@@ -71,12 +84,37 @@ internal class SeverityHandler(
     return advice.any(bySourceSets) || (spec.first.isFail() && globalAdvice.isNotEmpty())
   }
 
-  fun shouldFailPlugins(pluginAdvice: Set<PluginAdvice>): Boolean {
-    return (redundantPluginsBehavior.isFail() || anyBehavior.first.isFail()) && pluginAdvice.isNotEmpty()
-  }
+  private fun shouldFailForDuplicateClasses(
+    spec: Pair<Behavior, List<Behavior>>,
+    duplicateClasses: Set<DuplicateClass>,
+  ): Boolean {
+    // Seed the "global" warnings with the set of all possible warnings. Later on we'll drain this set as elements of it
+    // are  "consumed" by sourceSet-specific behaviors.
+    val globalAdvice = duplicateClasses.toMutableSet()
 
-  fun shouldFailModuleStructure(moduleAdvice: Set<ModuleAdvice>): Boolean {
-    return (moduleStructureBehavior.isFail() || anyBehavior.first.isFail()) && ModuleAdvice.isNotEmpty(moduleAdvice)
+    val bySourceSets: (DuplicateClass) -> Boolean = { d ->
+      // These are the custom behaviors, if any, associated with the source sets represented by this warning.
+      val behaviors = spec.second.filter { b ->
+        b.sourceSetName == DependencyScope.sourceSetName(d.classpathName)
+      }
+
+      // Looking for a match between sourceSet-specific behavior and warning.
+      var shouldFail = false
+      behaviors.forEach { b ->
+        val s = b.sourceSetName.lowercase()
+        val from = d.classpathName.lowercase().startsWith(s)
+
+        if (from) {
+          shouldFail = shouldFail || b.isFail()
+          globalAdvice.remove(d)
+        }
+      }
+
+      shouldFail
+    }
+
+    // If all advice is sourceSet-specific, then globalAdvice will be empty.
+    return duplicateClasses.any(bySourceSets) || (spec.first.isFail() && globalAdvice.isNotEmpty())
   }
 
   private fun Behavior.isFail(): Boolean = this is Fail
diff --git a/src/main/kotlin/com/autonomousapps/model/DuplicateClass.kt b/src/main/kotlin/com/autonomousapps/model/DuplicateClass.kt
index 50a917b2c..cb9af41ca 100644
--- a/src/main/kotlin/com/autonomousapps/model/DuplicateClass.kt
+++ b/src/main/kotlin/com/autonomousapps/model/DuplicateClass.kt
@@ -1,5 +1,6 @@
 package com.autonomousapps.model
 
+import com.autonomousapps.extension.Behavior
 import com.autonomousapps.internal.utils.LexicographicIterableComparator
 import com.autonomousapps.model.declaration.Variant
 import com.squareup.moshi.JsonClass
@@ -25,6 +26,12 @@ data class DuplicateClass(
     const val RUNTIME_CLASSPATH_NAME = "runtime"
   }
 
+  private val dotty = className.replace('/', '.')
+
+  internal fun containsMatchIn(behavior: Behavior): Boolean {
+    return behavior.filter.contains(className) || behavior.filter.contains(dotty)
+  }
+
   override fun compareTo(other: DuplicateClass): Int {
     return compareBy(DuplicateClass::variant)
       .thenBy(DuplicateClass::classpathName)
diff --git a/src/main/kotlin/com/autonomousapps/services/GlobalDslService.kt b/src/main/kotlin/com/autonomousapps/services/GlobalDslService.kt
index 81fa36425..953b39a61 100644
--- a/src/main/kotlin/com/autonomousapps/services/GlobalDslService.kt
+++ b/src/main/kotlin/com/autonomousapps/services/GlobalDslService.kt
@@ -238,6 +238,10 @@ abstract class GlobalDslService @Inject constructor(
     return issuesFor(projectPath) { it.unusedAnnotationProcessorsIssue }
   }
 
+  internal fun onDuplicateClassWarnings(projectPath: String): List<Provider<Behavior>> {
+    return issuesFor(projectPath) { it.duplicateClassWarningsIssue }
+  }
+
   internal fun redundantPluginsIssueFor(projectPath: String): Provider<Behavior> {
     return overlay(all.redundantPluginsIssue, projects.findByName(projectPath)?.redundantPluginsIssue)
   }
diff --git a/src/main/kotlin/com/autonomousapps/subplugin/ProjectPlugin.kt b/src/main/kotlin/com/autonomousapps/subplugin/ProjectPlugin.kt
index 8444786f3..b17c2ed8d 100644
--- a/src/main/kotlin/com/autonomousapps/subplugin/ProjectPlugin.kt
+++ b/src/main/kotlin/com/autonomousapps/subplugin/ProjectPlugin.kt
@@ -1035,6 +1035,7 @@ internal class ProjectPlugin(private val project: Project) {
         compileOnlyBehavior.addAll(compileOnlyIssueFor(theProjectPath))
         runtimeOnlyBehavior.addAll(runtimeOnlyIssueFor(theProjectPath))
         unusedProcsBehavior.addAll(unusedAnnotationProcessorsIssueFor(theProjectPath))
+        duplicateClassWarningsBehavior.addAll(onDuplicateClassWarnings(theProjectPath))
 
         // These don't have sourceSet-specific behaviors
         redundantPluginsBehavior.set(redundantPluginsIssueFor(theProjectPath))
diff --git a/src/main/kotlin/com/autonomousapps/tasks/FilterAdviceTask.kt b/src/main/kotlin/com/autonomousapps/tasks/FilterAdviceTask.kt
index ee1bb9814..96f4ac035 100644
--- a/src/main/kotlin/com/autonomousapps/tasks/FilterAdviceTask.kt
+++ b/src/main/kotlin/com/autonomousapps/tasks/FilterAdviceTask.kt
@@ -2,16 +2,15 @@
 // SPDX-License-Identifier: Apache-2.0
 package com.autonomousapps.tasks
 
-import com.autonomousapps.model.PluginAdvice
 import com.autonomousapps.extension.Behavior
 import com.autonomousapps.extension.Ignore
 import com.autonomousapps.extension.Issue
 import com.autonomousapps.internal.DependencyScope
 import com.autonomousapps.internal.advice.SeverityHandler
-import com.autonomousapps.internal.utils.*
-import com.autonomousapps.model.Advice
-import com.autonomousapps.model.ModuleAdvice
-import com.autonomousapps.model.ProjectAdvice
+import com.autonomousapps.internal.utils.bufferWriteJson
+import com.autonomousapps.internal.utils.fromJson
+import com.autonomousapps.internal.utils.getAndDelete
+import com.autonomousapps.model.*
 import org.gradle.api.DefaultTask
 import org.gradle.api.file.RegularFileProperty
 import org.gradle.api.provider.ListProperty
@@ -62,6 +61,9 @@ abstract class FilterAdviceTask @Inject constructor(
   @get:Input
   abstract val runtimeOnlyBehavior: ListProperty<Behavior>
 
+  @get:Input
+  abstract val duplicateClassWarningsBehavior: ListProperty<Behavior>
+
   @get:Input
   abstract val redundantPluginsBehavior: Property<Behavior>
 
@@ -83,6 +85,7 @@ abstract class FilterAdviceTask @Inject constructor(
       unusedProcsBehavior.set(this@FilterAdviceTask.unusedProcsBehavior)
       compileOnlyBehavior.set(this@FilterAdviceTask.compileOnlyBehavior)
       runtimeOnlyBehavior.set(this@FilterAdviceTask.runtimeOnlyBehavior)
+      duplicateClassWarningsBehavior.set(this@FilterAdviceTask.duplicateClassWarningsBehavior)
       redundantPluginsBehavior.set(this@FilterAdviceTask.redundantPluginsBehavior)
       moduleStructureBehavior.set(this@FilterAdviceTask.moduleStructureBehavior)
       output.set(this@FilterAdviceTask.output)
@@ -100,6 +103,7 @@ abstract class FilterAdviceTask @Inject constructor(
     val unusedProcsBehavior: ListProperty<Behavior>
     val compileOnlyBehavior: ListProperty<Behavior>
     val runtimeOnlyBehavior: ListProperty<Behavior>
+    val duplicateClassWarningsBehavior: ListProperty<Behavior>
     val redundantPluginsBehavior: Property<Behavior>
     val moduleStructureBehavior: Property<Behavior>
     val output: RegularFileProperty
@@ -117,6 +121,7 @@ abstract class FilterAdviceTask @Inject constructor(
     private val unusedProcsBehavior = partition(parameters.unusedProcsBehavior.get())
     private val compileOnlyBehavior = partition(parameters.compileOnlyBehavior.get())
     private val runtimeOnlyBehavior = partition(parameters.runtimeOnlyBehavior.get())
+    private val duplicateClassWarningsBehavior = partition(parameters.duplicateClassWarningsBehavior.get())
 
     private val redundantPluginsBehavior = parameters.redundantPluginsBehavior.get()
     private val moduleStructureBehavior = parameters.moduleStructureBehavior.get()
@@ -162,7 +167,11 @@ abstract class FilterAdviceTask @Inject constructor(
         .filterNot {
           moduleStructureBehavior is Ignore || it.shouldIgnore(moduleStructureBehavior)
         }
-        .toSet()
+        .toSortedSet()
+
+      val duplicateClassWarnings = projectAdvice.warning.duplicateClasses.asSequence()
+        .filterOf(duplicateClassWarningsBehavior)
+        .toSortedSet()
 
       val severityHandler = SeverityHandler(
         anyBehavior = anyBehavior,
@@ -171,18 +180,20 @@ abstract class FilterAdviceTask @Inject constructor(
         incorrectConfigurationBehavior = incorrectConfigurationBehavior,
         unusedProcsBehavior = unusedProcsBehavior,
         compileOnlyBehavior = compileOnlyBehavior,
+        duplicateClassWarningsBehavior = duplicateClassWarningsBehavior,
         redundantPluginsBehavior = redundantPluginsBehavior,
         moduleStructureBehavior = moduleStructureBehavior,
       )
       val shouldFailDeps = severityHandler.shouldFailDeps(dependencyAdvice)
       val shouldFailPlugins = severityHandler.shouldFailPlugins(pluginAdvice)
       val shouldFailModuleStructure = severityHandler.shouldFailModuleStructure(moduleAdvice)
+      val shouldFailDuplicateClasses = severityHandler.shouldFailDuplicateClasses(duplicateClassWarnings)
 
       val filteredAdvice = projectAdvice.copy(
         dependencyAdvice = dependencyAdvice,
         pluginAdvice = pluginAdvice,
         moduleAdvice = moduleAdvice,
-        shouldFail = shouldFailDeps || shouldFailPlugins || shouldFailModuleStructure
+        shouldFail = shouldFailDeps || shouldFailPlugins || shouldFailModuleStructure || shouldFailDuplicateClasses
       )
 
       output.bufferWriteJson(filteredAdvice)
@@ -238,6 +249,37 @@ abstract class FilterAdviceTask @Inject constructor(
       }
       else this
     }
+
+    private fun Sequence<DuplicateClass>.filterOf(
+      behaviorSpec: Pair<Behavior, List<Behavior>>,
+    ): Sequence<DuplicateClass> {
+      val globalBehavior = behaviorSpec.first
+      val sourceSetsBehavior = behaviorSpec.second
+
+      val byGlobal: (DuplicateClass) -> Boolean = { d ->
+        globalBehavior is Ignore
+          || d.containsMatchIn(globalBehavior)
+      }
+
+      val bySourceSets: (DuplicateClass) -> Boolean = { d ->
+        // These are the custom behaviors, if any, associated with the source sets represented by this warning.
+        val behaviors = sourceSetsBehavior.filter { b ->
+          b.sourceSetName == DependencyScope.sourceSetName(d.classpathName)
+        }
+
+        // reduce() will fail on an empty collection, so use reduceOrNull().
+        behaviors.map {
+          it is Ignore
+            || d.containsMatchIn(it)
+        }.reduceOrNull { acc, b ->
+          acc || b
+        } ?: false
+      }
+
+      return filterNot { duplicateClass ->
+        (byGlobal(duplicateClass) || bySourceSets(duplicateClass))
+      }
+    }
   }
 
   companion object {