diff --git a/src/libraries/JANA/Services/JParameterManager.h b/src/libraries/JANA/Services/JParameterManager.h
index 70255898d..291407974 100644
--- a/src/libraries/JANA/Services/JParameterManager.h
+++ b/src/libraries/JANA/Services/JParameterManager.h
@@ -366,6 +366,7 @@ template<typename T>
 inline void JParameterManager::Parse(const std::string& value, std::vector<T> &val) {
     std::stringstream ss(value);
     std::string s;
+    val.clear(); // clearing the input vector to ensure no dulication which can be caused due to val.push_back(t);
     while (getline(ss, s, ',')) {
         T t;
         Parse(s, t);
diff --git a/src/programs/tests/JParameterManagerTests.cc b/src/programs/tests/JParameterManagerTests.cc
index b509d6eda..89c3c8ea0 100644
--- a/src/programs/tests/JParameterManagerTests.cc
+++ b/src/programs/tests/JParameterManagerTests.cc
@@ -195,6 +195,7 @@ TEST_CASE("JParameterManager_VectorParams") {
         std::vector<std::string> outputs;
         auto param = jpm.GetParameter("test", outputs);
         REQUIRE(param->GetValue() == "first,second one, third one ");
+        REQUIRE(inputs.size()==3); // an additional test to see that the size of the input vector remains the same: Issue #256
     }
     SECTION("Reading a vector of ints") {
         jpm.SetParameter("test", "1,2, 3 ");