diff --git a/src/IO/MultiDynamicDiscretisedDensityOutputFileFormat.cxx b/src/IO/MultiDynamicDiscretisedDensityOutputFileFormat.cxx
index 4542fcabd..7ee8c09dc 100644
--- a/src/IO/MultiDynamicDiscretisedDensityOutputFileFormat.cxx
+++ b/src/IO/MultiDynamicDiscretisedDensityOutputFileFormat.cxx
@@ -93,7 +93,7 @@ MultiDynamicDiscretisedDensityOutputFileFormat::actual_write_to_file(std::string
   // Create all the filenames
   VectorWithOffset<std::string> individual_filenames(1, int(density.get_num_time_frames()));
   for (int i = 1; i <= int(density.get_num_time_frames()); i++)
-    individual_filenames[i] = filename + "_" + boost::lexical_cast<std::string>(i);
+    individual_filenames[i] = filename + "_" + std::to_string(i);
 
   // Write each individual image
   for (int i = 1; i <= int(density.get_num_time_frames()); i++)
diff --git a/src/IO/MultiParametricDiscretisedDensityOutputFileFormat.cxx b/src/IO/MultiParametricDiscretisedDensityOutputFileFormat.cxx
index 126c5bd5f..b065304d8 100644
--- a/src/IO/MultiParametricDiscretisedDensityOutputFileFormat.cxx
+++ b/src/IO/MultiParametricDiscretisedDensityOutputFileFormat.cxx
@@ -106,7 +106,7 @@ ParamDiscDensityOutputFileFormat::actual_write_to_file(std::string& filename,
   // Create all the filenames
   VectorWithOffset<std::string> individual_filenames(1, int(density.get_num_params()));
   for (int i = 1; i <= int(density.get_num_params()); i++)
-    individual_filenames[i] = filename + "_" + boost::lexical_cast<std::string>(i);
+    individual_filenames[i] = filename + "_" + std::to_string(i);
 
   // Write each individual image
   for (int i = 1; i <= int(density.get_num_params()); i++)
diff --git a/src/include/stir/common.h b/src/include/stir/common.h
index 5a501a040..c28a0456d 100644
--- a/src/include/stir/common.h
+++ b/src/include/stir/common.h
@@ -72,7 +72,9 @@
 #include <cstring>
 #include <cmath>
 #include <cassert>
-#include <boost/math/constants/constants.hpp>
+#if __cplusplus >= 202002L
+#  include <numbers>
+#endif
 
 //*************** namespace macros
 #define START_NAMESPACE_STIR                                                                                                     \
@@ -128,10 +130,16 @@
 //***************
 START_NAMESPACE_STIR
 
+#ifndef _PI
+#  if __cplusplus >= 202002L
 //! The constant pi to high precision.
 /*! \ingroup buildblock */
-#ifndef _PI
-#  define _PI boost::math::constants::pi<double>()
+#    define _PI std::numbers::pi
+#  else
+//! The constant pi to high precision.
+/*! \ingroup buildblock */
+#    define _PI 3.1415926535897932384626433832795028841971693993751058209749445923078164062
+#  endif
 #endif
 
 //! Define the speed of light in mm / ps
diff --git a/src/include/stir/recon_buildblock/ML_estimate_component_based_normalisation.h b/src/include/stir/recon_buildblock/ML_estimate_component_based_normalisation.h
index f7fa35ce6..9fcbc0650 100644
--- a/src/include/stir/recon_buildblock/ML_estimate_component_based_normalisation.h
+++ b/src/include/stir/recon_buildblock/ML_estimate_component_based_normalisation.h
@@ -9,10 +9,11 @@
 /*!
  \file
  \ingroup recon_buildblock
- \brief Declaration of ML_estimate_component_based_normalisation
+ \brief Declaration of stir::ML_estimate_component_based_normalisation
  \author Kris Thielemans
  */
 #include "stir/common.h"
+#include <string>
 
 START_NAMESPACE_STIR
 
diff --git a/src/include/stir/warning.h b/src/include/stir/warning.h
index 7d7fc5678..317aee04b 100644
--- a/src/include/stir/warning.h
+++ b/src/include/stir/warning.h
@@ -17,11 +17,9 @@
   \author Kris Thielemans
 
 */
-#include "stir/common.h"
 #include "stir/Verbosity.h"
-#include <iostream>
-
-#include "TextWriter.h"
+#include "stir/TextWriter.h"
+#include <sstream>
 
 START_NAMESPACE_STIR
 
diff --git a/src/recon_buildblock/BinNormalisationSPECT.cxx b/src/recon_buildblock/BinNormalisationSPECT.cxx
index 43971d715..5b3ec1689 100644
--- a/src/recon_buildblock/BinNormalisationSPECT.cxx
+++ b/src/recon_buildblock/BinNormalisationSPECT.cxx
@@ -318,7 +318,7 @@ BinNormalisationSPECT::read_uniformity_table(Array<3, float>& uniformity) const
   for (int n = 1; n <= num_detector_heads; n++)
     {
 
-      const std::string n_string = boost::lexical_cast<std::string>(n);
+      const std::string n_string = std::to_string(n);
       const std::string filename(this->folder_prefix + n_string + "/" + uniformity_filename);
 
       std::ifstream input(filename.c_str());