diff --git a/src/test/fuzz/util.h b/src/test/fuzz/util.h
--- a/src/test/fuzz/util.h
+++ b/src/test/fuzz/util.h
@@ -325,8 +325,8 @@
             return 0;
         }
         std::memcpy(buf, random_bytes.data(), random_bytes.size());
-        if (AdditionOverflow((uint64_t)fuzzed_file->m_offset,
-                             random_bytes.size())) {
+        if (AdditionOverflow(fuzzed_file->m_offset,
+                             int64_t(random_bytes.size()))) {
             return fuzzed_file->m_fuzzed_data_provider.ConsumeBool() ? 0 : -1;
         }
         fuzzed_file->m_offset += random_bytes.size();
@@ -338,7 +338,7 @@
         const ssize_t n =
             fuzzed_file->m_fuzzed_data_provider.ConsumeIntegralInRange<ssize_t>(
                 0, size);
-        if (AdditionOverflow(fuzzed_file->m_offset, n)) {
+        if (AdditionOverflow(fuzzed_file->m_offset, int64_t(n))) {
             return fuzzed_file->m_fuzzed_data_provider.ConsumeBool() ? 0 : -1;
         }
         fuzzed_file->m_offset += n;