diff --git a/tests/gtest/avif_fuzztest_properties.cc b/tests/gtest/avif_fuzztest_properties.cc
index 1a98d7acc3..7865d14aa8 100644
--- a/tests/gtest/avif_fuzztest_properties.cc
+++ b/tests/gtest/avif_fuzztest_properties.cc
@@ -37,12 +37,15 @@ void EncodeDecode(ImagePtr image, EncoderPtr encoder, DecoderPtr decoder,
       ASSERT_EQ(
           avifImageAddUUIDProperty(image.get(), testProp.uuid.data(),
                                    testProp.body.data(), testProp.body.size()),
-          AVIF_RESULT_OK);
+          avifIsValidUUID(testProp.uuid.data()) ? AVIF_RESULT_OK
+                                                : AVIF_RESULT_INVALID_ARGUMENT);
     } else {
       ASSERT_EQ(avifImageAddOpaqueProperty(image.get(), testProp.fourcc.data(),
                                            testProp.body.data(),
                                            testProp.body.size()),
-                AVIF_RESULT_OK);
+                avifIsKnownPropertyType(testProp.fourcc.data())
+                    ? AVIF_RESULT_INVALID_ARGUMENT
+                    : AVIF_RESULT_OK);
     }
   }
 
@@ -74,22 +77,14 @@ inline auto ArbitraryProp() {
   auto fourcc = fuzztest::Arbitrary<std::array<uint8_t, 4>>();
   auto uuid = fuzztest::Arbitrary<std::array<uint8_t, 16>>();  // ignored
   auto body = fuzztest::Arbitrary<std::vector<uint8_t>>();
-  // Don't return known properties.
-  return fuzztest::Filter(
-      [](const TestProp& prop) {
-        return !avifIsKnownPropertyType(prop.fourcc.data());
-      },
-      fuzztest::StructOf<TestProp>(fourcc, uuid, body));
+  return fuzztest::StructOf<TestProp>(fourcc, uuid, body);
 }
 
 inline auto ArbitraryUUIDProp() {
   auto fourcc = fuzztest::Just(std::array<uint8_t, 4>{'u', 'u', 'i', 'd'});
   auto uuid = fuzztest::Arbitrary<std::array<uint8_t, 16>>();
   auto body = fuzztest::Arbitrary<std::vector<uint8_t>>();
-  // Don't use invalid UUIDs.
-  return fuzztest::Filter(
-      [](const TestProp& prop) { return avifIsValidUUID(prop.uuid.data()); },
-      fuzztest::StructOf<TestProp>(fourcc, uuid, body));
+  return fuzztest::StructOf<TestProp>(fourcc, uuid, body);
 }
 
 inline auto ArbitraryProps() {