diff --git a/CHANGELOG.md b/CHANGELOG.md
index 00e37aa88f07..ed674a70fd2c 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -23,6 +23,7 @@
 - [[PR 1172]](https://github.com/parthenon-hpc-lab/parthenon/pull/1172) Make parthenon manager robust against external MPI init and finalize calls
 
 ### Fixed (not changing behavior/API/variables/...)
+- [[PR 1215]](https://github.com/parthenon-hpc-lab/parthenon/pull/1215) Fix issue with uninitialized input parameter block data
 - [[PR 1211]](https://github.com/parthenon-hpc-lab/parthenon/pull/1211) remove inline from WriteTaskGraph
 - [[PR 1188]](https://github.com/parthenon-hpc-lab/parthenon/pull/1188) Fix hdf5 output issue for metadata none variables, update test.
 - [[PR 1170]](https://github.com/parthenon-hpc-lab/parthenon/pull/1170) Fixed incorrect initialization of array by a const not constexpr
diff --git a/src/parameter_input.cpp b/src/parameter_input.cpp
index dc6651e0b24c..b04ee738527f 100644
--- a/src/parameter_input.cpp
+++ b/src/parameter_input.cpp
@@ -3,7 +3,7 @@
 // Copyright(C) 2014 James M. Stone <jmstone@princeton.edu> and other code contributors
 // Licensed under the 3-clause BSD License, see LICENSE file for details
 //========================================================================================
-// (C) (or copyright) 2020-2023. Triad National Security, LLC. All rights reserved.
+// (C) (or copyright) 2020-2024. Triad National Security, LLC. All rights reserved.
 //
 // This program was produced under U.S. Government contract 89233218CNA000001 for Los
 // Alamos National Laboratory (LANL), which is operated by Triad National Security, LLC
@@ -277,6 +277,10 @@ InputBlock *ParameterInput::FindOrAddBlock(const std::string &name) {
   pib->pline = nullptr;         // Terminate the InputLine list
   pib->pnext = nullptr;         // Terminate the InputBlock list
 
+  // Default max lengths to zero (in case of no parameters in this block)
+  pib->max_len_parname = 0;
+  pib->max_len_parvalue = 0;
+
   // if this is the first block in list, save pointer to it in class
   if (pfirst_block == nullptr) {
     pfirst_block = pib;