diff --git a/poet/include/PhreeqcMatrix.hpp b/poet/include/PhreeqcMatrix.hpp
index 08a1f47f..ad8f6b1a 100644
--- a/poet/include/PhreeqcMatrix.hpp
+++ b/poet/include/PhreeqcMatrix.hpp
@@ -9,6 +9,7 @@
 #include <vector>
 
 #include "IPhreeqc.hpp"
+#include "global_structures.h"
 
 /**
  * @brief Class for storing information from Phreeqc
@@ -258,6 +259,15 @@ public:
    */
   std::string getDatabase() const;
 
+  /**
+   * @brief Check if a cell with given ID exists in the PhreeqcMatrix.
+   *
+   * @param cell_id ID of the cell (user id from Phreeqc script) to check for.
+   * @return true Entry exists
+   * @return false Entry doesn't exist
+   */
+  bool checkIfExists(int cell_id) const;
+
 private:
   std::map<int, std::vector<element>> _m_map;
   std::map<int, std::vector<base_names>> _m_internal_names;
diff --git a/poet/src/PhreeqcMatrix/Misc.cpp b/poet/src/PhreeqcMatrix/Misc.cpp
index fffe8ad8..e5d7d515 100644
--- a/poet/src/PhreeqcMatrix/Misc.cpp
+++ b/poet/src/PhreeqcMatrix/Misc.cpp
@@ -1,5 +1,4 @@
 #include "PhreeqcMatrix.hpp"
-#include <cstddef>
 
 std::vector<int> PhreeqcMatrix::getIds() const {
   std::vector<int> ids;
@@ -50,4 +49,8 @@ std::string PhreeqcMatrix::getDumpStringsPQI(int cell_id) const {
   return dump_string;
 }
 
-std::string PhreeqcMatrix::getDatabase() const { return _m_database; }
\ No newline at end of file
+std::string PhreeqcMatrix::getDatabase() const { return _m_database; }
+
+bool PhreeqcMatrix::checkIfExists(int cell_id) const {
+  return this->_m_map.find(cell_id) != this->_m_map.end();
+}
\ No newline at end of file
diff --git a/poet/test/testPhreeqcMatrix.cpp b/poet/test/testPhreeqcMatrix.cpp
index dda31d60..55fa3e9b 100644
--- a/poet/test/testPhreeqcMatrix.cpp
+++ b/poet/test/testPhreeqcMatrix.cpp
@@ -21,6 +21,9 @@ POET_TEST(PhreeqcMatrixOneSolution) {
   EXPECT_EQ(ids.size(), 1);
   EXPECT_EQ(ids[0], 1);
 
+  EXPECT_TRUE(pqc_mat.checkIfExists(1));
+  EXPECT_FALSE(pqc_mat.checkIfExists(2));
+
   PhreeqcMatrix::STLExport exported_init = pqc_mat.get();
   // ID + H,O,Charge,H(0),O(0) + 4 Solutions + 4 Equil incl. params
   EXPECT_EQ(exported_init.names.size(), 14);