diff --git a/src/test/jtx/impl/mpt.cpp b/src/test/jtx/impl/mpt.cpp
index fc831790f1..d7b4a1570e 100644
--- a/src/test/jtx/impl/mpt.cpp
+++ b/src/test/jtx/impl/mpt.cpp
@@ -644,7 +644,7 @@ MPTTester::operator[](std::string const& name) const
 }
 
 PrettyAmount
-MPTTester::operator()(std::uint64_t amount) const
+MPTTester::operator()(std::int64_t amount) const
 {
     return MPT("", issuanceID())(amount);
 }
diff --git a/src/test/jtx/mpt.h b/src/test/jtx/mpt.h
index f9c58ebc9e..e3097b28b0 100644
--- a/src/test/jtx/mpt.h
+++ b/src/test/jtx/mpt.h
@@ -272,7 +272,7 @@ public:
     operator[](std::string const& name) const;
 
     PrettyAmount
-    operator()(std::uint64_t amount) const;
+    operator()(std::int64_t amount) const;
 
     operator Asset() const;