diff --git a/src/poly/solver/private/polySolver.cpp b/src/poly/solver/private/polySolver.cpp
index 96da470..c83c478 100644
--- a/src/poly/solver/private/polySolver.cpp
+++ b/src/poly/solver/private/polySolver.cpp
@@ -41,14 +41,14 @@
 
 namespace laneEmden {
 
-    double a (int k, double n) { // NOLINT(*-no-recursion)
+    double a (const int k, const double n) { // NOLINT(*-no-recursion)
         if ( k == 0 ) { return 1; }
         if ( k == 1 ) { return 0; }
         else { return -(c(k-2, n)/(std::pow(k, 2)+k)); }
 
     }
 
-    double c(int m, double n) { // NOLINT(*-no-recursion)
+    double c(const int m, const double n) { // NOLINT(*-no-recursion)
         if ( m == 0 ) { return std::pow(a(0, n), n); }
         else {
             double termOne = 1.0/(m*a(0, n));
@@ -60,7 +60,7 @@ namespace laneEmden {
         }
     }
 
-    double thetaSeriesExpansion(double xi, double n, int order) {
+    double thetaSeriesExpansion(const double xi, const double n, const int order) {
         double acc = 0;
         for (int k = 0; k < order; k++) {
             acc += a(k, n) * std::pow(xi, k);
diff --git a/src/poly/solver/public/polySolver.h b/src/poly/solver/public/polySolver.h
index ecc1597..ca1d02a 100644
--- a/src/poly/solver/public/polySolver.h
+++ b/src/poly/solver/public/polySolver.h
@@ -33,9 +33,9 @@
 
 
 namespace laneEmden {
-    double a (int k, double n);
-    double c(int m, double n);
-    double thetaSeriesExpansion(double xi, double n, int order);
+    double a (const int k, const double n);
+    double c(const int m, const double n);
+    double thetaSeriesExpansion(const double xi, const double n, const int order);
 }
 
 // Struct to persist lifetime of the linear and nonlinear solvers