diff --git a/core/metacling/test/TClingTests.cxx b/core/metacling/test/TClingTests.cxx
index 171bd3322092c..ad3582be3082f 100644
--- a/core/metacling/test/TClingTests.cxx
+++ b/core/metacling/test/TClingTests.cxx
@@ -435,3 +435,19 @@ TEST_F(TClingTests, UndeclaredIdentifierCrash)
    diagRAII.requiredDiag(kError, "cling", expectedError, false);
    gInterpreter->ProcessLine("for(i=0; i < 0;); // the second usage of `i` was enough to get a segfault");
 }
+
+// https://github.com/root-project/root/issues/15818
+TEST_F(TClingTests, VeryLongExpression)
+{
+   std::string expression = R"(
+namespace R_rdf {
+auto func0(const int var0){return var0 )";
+   for (unsigned short  i = 0; i < 4096; ++i)
+      expression += "+ var0 ";
+   expression += R"( > 0
+;}
+using func0_ret_t = typename ROOT::TypeTraits::CallableTraits<decltype(func0)>::ret_type;
+})";
+   auto res = gInterpreter->Declare(expression.c_str());
+   EXPECT_TRUE(res);
+}