diff --git a/api/19/src/test/java/com/toasttab/android/Api19SignaturesTest.kt b/api/19/src/test/java/com/toasttab/android/Api19SignaturesTest.kt
new file mode 100644
index 0000000..7605250
--- /dev/null
+++ b/api/19/src/test/java/com/toasttab/android/Api19SignaturesTest.kt
@@ -0,0 +1,77 @@
+/*
+ * Copyright (c) 2023. Toast Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.toasttab.android
+
+import org.codehaus.mojo.animal_sniffer.Clazz
+import org.junit.Test
+import strikt.api.expectThat
+import strikt.assertions.all
+import strikt.assertions.contains
+import strikt.assertions.isA
+import strikt.assertions.isNotNull
+import java.io.File
+import java.io.ObjectInputStream
+import java.util.zip.GZIPInputStream
+
+class Api19SignaturesTest {
+    @Test
+    fun `signatures include Integer#hashCode(int)`() {
+        val desc = ObjectInputStream(GZIPInputStream(File(System.getProperty("signatures")).inputStream())).use {
+            generateSequence { it.readObject() as Clazz? }.toList()
+        }
+
+        val integer = desc.find { it.name == "java/lang/Integer" }
+
+        expectThat(integer).isNotNull().and {
+            get { signatures }.contains("hashCode(I)I")
+        }
+    }
+
+    @Test
+    fun `core lib signatures include Stream#count()`() {
+        val desc = ObjectInputStream(GZIPInputStream(File(System.getProperty("coreLibSignatures")).inputStream())).use {
+            generateSequence { it.readObject() as Clazz? }.toList()
+        }
+
+        val stream = desc.find { it.name == "java/util/stream/Stream" }
+
+        expectThat(stream).isNotNull().and {
+            get { signatures }.contains("count()J")
+        }
+    }
+
+    @Test
+    fun `signatures use HashSet`() {
+        val desc = ObjectInputStream(GZIPInputStream(File(System.getProperty("signatures")).inputStream())).use {
+            generateSequence { it.readObject() as Clazz? }.toList()
+        }
+
+        expectThat(desc).all {
+            get { signatures }.isA<HashSet<*>>()
+        }
+    }
+
+    @Test
+    fun `core lib signatures use HashSet`() {
+        val desc = ObjectInputStream(GZIPInputStream(File(System.getProperty("coreLibSignatures")).inputStream())).use {
+            generateSequence { it.readObject() as Clazz? }.toList()
+        }
+
+        expectThat(desc).all {
+            get { signatures }.isA<HashSet<*>>()
+        }
+    }
+}
diff --git a/buildSrc/src/main/kotlin/signatures-conventions.gradle.kts b/buildSrc/src/main/kotlin/signatures-conventions.gradle.kts
index c6cea83..27f48cf 100644
--- a/buildSrc/src/main/kotlin/signatures-conventions.gradle.kts
+++ b/buildSrc/src/main/kotlin/signatures-conventions.gradle.kts
@@ -65,6 +65,7 @@ dependencies {
     testImplementation(libs.strikt.core)
     testImplementation(libs.expediter.core)
     testImplementation(libs.protobuf.java)
+    testImplementation(libs.animalSniffer)
 }
 
 tasks.register<TypeDescriptorsTask>(Tasks.signatures) {
@@ -91,6 +92,7 @@ publishing.publications.named<MavenPublication>(Publications.MAIN) {
 tasks {
     test {
         fileProperty("platformDescriptors", layout.buildDirectory.file(Outputs.expediter))
+        fileProperty("signatures", layout.buildDirectory.file(Outputs.signatures))
         filesProperty("sdk", configurations.named(Configurations.SDK))
         filesProperty("jar", configurations.named(Configurations.EXERCISE_STANDARD_SUGAR))
 
diff --git a/buildSrc/src/main/kotlin/signatures-core-lib-conventions.gradle.kts b/buildSrc/src/main/kotlin/signatures-core-lib-conventions.gradle.kts
index c90159f..73c68e9 100644
--- a/buildSrc/src/main/kotlin/signatures-core-lib-conventions.gradle.kts
+++ b/buildSrc/src/main/kotlin/signatures-core-lib-conventions.gradle.kts
@@ -55,6 +55,7 @@ publishing.publications.named<MavenPublication>(Publications.MAIN) {
 tasks {
     test {
         fileProperty("platformCoreLibDescriptors", layout.buildDirectory.file(Outputs.expediterCoreLib))
+        fileProperty("coreLibSignatures", layout.buildDirectory.file(Outputs.signaturesCoreLib))
 
         dependsOn(Tasks.signaturesCoreLib)
     }
diff --git a/signature-builder/src/main/kotlin/com/toasttab/android/descriptors/sniffer/AnimalSnifferConverter.kt b/signature-builder/src/main/kotlin/com/toasttab/android/descriptors/sniffer/AnimalSnifferConverter.kt
index be1d53a..c2c03e0 100644
--- a/signature-builder/src/main/kotlin/com/toasttab/android/descriptors/sniffer/AnimalSnifferConverter.kt
+++ b/signature-builder/src/main/kotlin/com/toasttab/android/descriptors/sniffer/AnimalSnifferConverter.kt
@@ -22,7 +22,7 @@ import protokt.v1.toasttab.expediter.v1.TypeDescriptor
 object AnimalSnifferConverter {
     fun convert(type: TypeDescriptor) = Clazz(
         type.name,
-        (type.fields.map(AnimalSnifferConverter::fieldSignature) + type.methods.map(AnimalSnifferConverter::methodSignature)).toSet(),
+        (type.fields.map(AnimalSnifferConverter::fieldSignature) + type.methods.map(AnimalSnifferConverter::methodSignature)).toHashSet(),
         type.superName,
         type.interfaces.toTypedArray()
     )