diff --git a/.clusterfuzzlite/build.sh b/.clusterfuzzlite/build.sh
index 7db9375..8c7bc09 100644
--- a/.clusterfuzzlite/build.sh
+++ b/.clusterfuzzlite/build.sh
@@ -2,5 +2,16 @@
 # undocumented dependency
 go install github.com/AdamKorcz/go-118-fuzz-build@latest
 go get github.com/AdamKorcz/go-118-fuzz-build/utils
+
+# workaround https://github.com/AdamKorcz/go-118-fuzz-build/issues/2
+mv testonly/constants.go        testonly/constants_fuzz.go
+mv testonly/reference_test.go   testonly/reference_test_fuzz.go
+mv testonly/tree_test.go        testonly/tree_test_fuzz.go
+mv testonly/tree.go             testonly/tree_fuzz.go
+
 # necessary to list each fuzz test explicitly
 compile_native_go_fuzzer github.com/transparency-dev/merkle/compact FuzzRangeNodes FuzzRangeNodes
+compile_native_go_fuzzer github.com/transparency-dev/merkle/testonly FuzzConsistencyProofAndVerify FuzzConsistencyProofAndVerify
+compile_native_go_fuzzer github.com/transparency-dev/merkle/testonly FuzzInclusionProofAndVerify FuzzInclusionProofAndVerify
+compile_native_go_fuzzer github.com/transparency-dev/merkle/testonly FuzzHashAtAgainstReferenceImplementation FuzzHashAtAgainstReferenceImplementation
+compile_native_go_fuzzer github.com/transparency-dev/merkle/testonly FuzzInclusionProofAgainstReferenceImplementation FuzzInclusionProofAgainstReferenceImplementation
diff --git a/testonly/tree_fuzz_test.go b/testonly/tree_fuzz_test.go
index 9fcbbff..f884017 100644
--- a/testonly/tree_fuzz_test.go
+++ b/testonly/tree_fuzz_test.go
@@ -4,6 +4,7 @@ package testonly
 
 import (
 	"bytes"
+	"math"
 	"testing"
 
 	"github.com/google/go-cmp/cmp"
@@ -12,7 +13,7 @@ import (
 )
 
 // Compute and verify consistency proofs
-func FuzzConsistencyProof(f *testing.F) {
+func FuzzConsistencyProofAndVerify(f *testing.F) {
 	for size := 0; size <= 8; size++ {
 		for end := 0; end <= size; end++ {
 			for begin := 0; begin <= end; begin++ {
@@ -21,6 +22,10 @@ func FuzzConsistencyProof(f *testing.F) {
 		}
 	}
 	f.Fuzz(func(t *testing.T, size, begin, end uint64) {
+		// necessary to restrict size for compile_native_go_fuzzer
+		if size >= math.MaxUint16 {
+			return
+		}
 		t.Logf("size=%d, begin=%d, end=%d", size, begin, end)
 		if begin > end || end > size {
 			return
@@ -39,13 +44,16 @@ func FuzzConsistencyProof(f *testing.F) {
 }
 
 // Compute and verify inclusion proofs
-func FuzzInclusionProof(f *testing.F) {
+func FuzzInclusionProofAndVerify(f *testing.F) {
 	for size := 0; size <= 8; size++ {
 		for index := 0; index <= size; index++ {
 			f.Add(uint64(index), uint64(size))
 		}
 	}
 	f.Fuzz(func(t *testing.T, index, size uint64) {
+		if size >= math.MaxUint16 {
+			return
+		}
 		t.Logf("index=%d, size=%d", index, size)
 		if index >= size {
 			return
@@ -70,6 +78,9 @@ func FuzzHashAtAgainstReferenceImplementation(f *testing.F) {
 		}
 	}
 	f.Fuzz(func(t *testing.T, index, size uint64) {
+		if size >= math.MaxUint16 {
+			return
+		}
 		t.Logf("index=%d, size=%d", index, size)
 		if index >= size {
 			return
@@ -91,6 +102,9 @@ func FuzzInclusionProofAgainstReferenceImplementation(f *testing.F) {
 		}
 	}
 	f.Fuzz(func(t *testing.T, index, size uint64) {
+		if size >= math.MaxUint16 {
+			return
+		}
 		t.Logf("index=%d, size=%d", index, size)
 		if index >= size {
 			return