diff --git a/src/angle_hybrid.cpp b/src/angle_hybrid.cpp
index f0e9002ace..7419139942 100644
--- a/src/angle_hybrid.cpp
+++ b/src/angle_hybrid.cpp
@@ -20,7 +20,6 @@
 #include "memory.h"
 #include "neighbor.h"
 
-#include <cctype>
 #include <cstring>
 
 using namespace LAMMPS_NS;
diff --git a/src/atom.h b/src/atom.h
index 944e0e1484..e8b1330651 100644
--- a/src/atom.h
+++ b/src/atom.h
@@ -21,9 +21,10 @@
 
 namespace LAMMPS_NS {
 
-// forward declaration
+// forward declarations
 
 class AtomVec;
+class Molecule;
 
 class Atom : protected Pointers {
  public:
@@ -252,7 +253,7 @@ class Atom : protected Pointers {
   // 1st molecule in template stores nset = # in set
 
   int nmolecule;
-  class Molecule **molecules;
+  Molecule **molecules;
 
   // type label maps
 
@@ -354,7 +355,7 @@ class Atom : protected Pointers {
   void add_molecule(int, char **);
   int find_molecule(const char *);
   std::vector<Molecule *> get_molecule_by_id(const std::string &);
-  void add_molecule_atom(class Molecule *, int, int, tagint);
+  void add_molecule_atom(Molecule *, int, int, tagint);
 
   void add_label_map();
 
diff --git a/src/atom_vec.cpp b/src/atom_vec.cpp
index e431488a39..bfda951823 100644
--- a/src/atom_vec.cpp
+++ b/src/atom_vec.cpp
@@ -20,12 +20,8 @@
 #include "fix.h"
 #include "force.h"
 #include "label_map.h"
-#include "math_const.h"
 #include "memory.h"
 #include "modify.h"
-#include "tokenizer.h"
-
-#include <cstring>
 
 using namespace LAMMPS_NS;
 
diff --git a/src/atom_vec_body.cpp b/src/atom_vec_body.cpp
index 6da3ee6671..538e9783df 100644
--- a/src/atom_vec_body.cpp
+++ b/src/atom_vec_body.cpp
@@ -22,6 +22,8 @@
 #include "modify.h"
 #include "my_pool_chunk.h"
 
+#include <cstring>
+
 using namespace LAMMPS_NS;
 
 /* ---------------------------------------------------------------------- */
diff --git a/src/atom_vec_ellipsoid.cpp b/src/atom_vec_ellipsoid.cpp
index c87179183c..59b8310d3f 100644
--- a/src/atom_vec_ellipsoid.cpp
+++ b/src/atom_vec_ellipsoid.cpp
@@ -25,6 +25,8 @@
 #include "memory.h"
 #include "modify.h"
 
+#include <cstring>
+
 using namespace LAMMPS_NS;
 using MathConst::MY_PI;
 
diff --git a/src/atom_vec_hybrid.cpp b/src/atom_vec_hybrid.cpp
index 5e70890414..c81ea56202 100644
--- a/src/atom_vec_hybrid.cpp
+++ b/src/atom_vec_hybrid.cpp
@@ -16,7 +16,6 @@
 #include "atom.h"
 #include "comm.h"
 #include "error.h"
-#include "tokenizer.h"
 
 #include <algorithm>
 #include <cstring>
diff --git a/src/atom_vec_line.cpp b/src/atom_vec_line.cpp
index 92cb994f96..ff09bed6d0 100644
--- a/src/atom_vec_line.cpp
+++ b/src/atom_vec_line.cpp
@@ -22,6 +22,7 @@
 #include "modify.h"
 
 #include <cmath>
+#include <cstring>
 
 using namespace LAMMPS_NS;
 using MathConst::MY_PI;
diff --git a/src/atom_vec_sphere.cpp b/src/atom_vec_sphere.cpp
index c18e68855c..d2f9c51880 100644
--- a/src/atom_vec_sphere.cpp
+++ b/src/atom_vec_sphere.cpp
@@ -20,6 +20,8 @@
 #include "math_const.h"
 #include "modify.h"
 
+#include <cstring>
+
 using namespace LAMMPS_NS;
 using namespace MathConst;
 
diff --git a/src/atom_vec_tri.cpp b/src/atom_vec_tri.cpp
index 6c66907518..a46609b02c 100644
--- a/src/atom_vec_tri.cpp
+++ b/src/atom_vec_tri.cpp
@@ -24,6 +24,7 @@
 #include "modify.h"
 
 #include <cmath>
+#include <cstring>
 
 using namespace LAMMPS_NS;
 using MathConst::MY_PI;
diff --git a/src/bond_hybrid.cpp b/src/bond_hybrid.cpp
index 1528c25fe8..4e477ab3a6 100644
--- a/src/bond_hybrid.cpp
+++ b/src/bond_hybrid.cpp
@@ -20,7 +20,6 @@
 #include "memory.h"
 #include "neighbor.h"
 
-#include <cctype>
 #include <cstring>
 
 using namespace LAMMPS_NS;
diff --git a/src/compute_angmom_chunk.h b/src/compute_angmom_chunk.h
index f86c69fc67..04023dbe44 100644
--- a/src/compute_angmom_chunk.h
+++ b/src/compute_angmom_chunk.h
@@ -23,6 +23,7 @@ ComputeStyle(angmom/chunk,ComputeAngmomChunk);
 #include "compute.h"
 
 namespace LAMMPS_NS {
+  class Fix;
 
 class ComputeAngmomChunk : public Compute {
  public:
@@ -34,8 +35,8 @@ class ComputeAngmomChunk : public Compute {
   void lock_enable() override;
   void lock_disable() override;
   int lock_length() override;
-  void lock(class Fix *, bigint, bigint) override;
-  void unlock(class Fix *) override;
+  void lock(Fix *, bigint, bigint) override;
+  void unlock(Fix *) override;
 
   double memory_usage() override;
 
diff --git a/src/compute_cluster_atom.cpp b/src/compute_cluster_atom.cpp
index 59139f4c68..0a0a36debd 100644
--- a/src/compute_cluster_atom.cpp
+++ b/src/compute_cluster_atom.cpp
@@ -17,7 +17,6 @@
 #include "comm.h"
 #include "error.h"
 #include "force.h"
-#include "group.h"
 #include "memory.h"
 #include "modify.h"
 #include "neigh_list.h"
diff --git a/src/compute_reduce.cpp b/src/compute_reduce.cpp
index 14c381c84d..f2afeab3e6 100644
--- a/src/compute_reduce.cpp
+++ b/src/compute_reduce.cpp
@@ -26,6 +26,7 @@
 #include "update.h"
 #include "variable.h"
 
+#include <cmath>
 #include <cstring>
 
 using namespace LAMMPS_NS;
diff --git a/src/compute_reduce_region.cpp b/src/compute_reduce_region.cpp
index f79e160684..efce00ff66 100644
--- a/src/compute_reduce_region.cpp
+++ b/src/compute_reduce_region.cpp
@@ -15,13 +15,11 @@
 
 #include "arg_info.h"
 #include "atom.h"
-#include "domain.h"
 #include "error.h"
 #include "fix.h"
 #include "group.h"
 #include "input.h"
 #include "memory.h"
-#include "modify.h"
 #include "region.h"
 #include "update.h"
 #include "variable.h"
diff --git a/src/create_atoms.cpp b/src/create_atoms.cpp
index 7fda4a4cdb..9c66d1d19b 100644
--- a/src/create_atoms.cpp
+++ b/src/create_atoms.cpp
@@ -38,7 +38,9 @@
 #include "text_file_reader.h"
 #include "variable.h"
 
+#include <cmath>
 #include <cstring>
+#include <exception>
 
 using namespace LAMMPS_NS;
 using MathConst::MY_2PI;
diff --git a/src/dihedral_hybrid.cpp b/src/dihedral_hybrid.cpp
index 734009b901..d38ccf5d52 100644
--- a/src/dihedral_hybrid.cpp
+++ b/src/dihedral_hybrid.cpp
@@ -20,7 +20,6 @@
 #include "memory.h"
 #include "neighbor.h"
 
-#include <cctype>
 #include <cstring>
 
 using namespace LAMMPS_NS;
diff --git a/src/domain.h b/src/domain.h
index 7d3194ccc9..1999baac2b 100644
--- a/src/domain.h
+++ b/src/domain.h
@@ -19,7 +19,6 @@
 #include <cmath>
 #include <map>
 #include <unordered_set>
-#include <vector>
 
 namespace LAMMPS_NS {
 class Region;
diff --git a/src/dump.cpp b/src/dump.cpp
index 93d9ee30bf..82a25c31f2 100644
--- a/src/dump.cpp
+++ b/src/dump.cpp
@@ -29,6 +29,7 @@
 #include "variable.h"
 
 #include <cstring>
+#include <stdexcept>
 
 using namespace LAMMPS_NS;
 
diff --git a/src/finish.cpp b/src/finish.cpp
index 3217d025f9..554f250fe1 100644
--- a/src/finish.cpp
+++ b/src/finish.cpp
@@ -24,8 +24,6 @@
 #include "memory.h"             // IWYU pragma: keep
 #include "min.h"
 #include "molecule.h"
-#include "neigh_list.h"
-#include "neigh_request.h"
 #include "neighbor.h"           // IWYU pragma: keep
 #include "output.h"
 #include "pair.h"
diff --git a/src/fix_ave_time.cpp b/src/fix_ave_time.cpp
index 0d1797fc6d..6c0397c74b 100644
--- a/src/fix_ave_time.cpp
+++ b/src/fix_ave_time.cpp
@@ -29,6 +29,7 @@
 #include "variable.h"
 
 #include <cstring>
+#include <stdexcept>
 
 using namespace LAMMPS_NS;
 using namespace FixConst;
diff --git a/src/fix_bond_history.h b/src/fix_bond_history.h
index 23d6a62d52..c9658acbd7 100644
--- a/src/fix_bond_history.h
+++ b/src/fix_bond_history.h
@@ -23,8 +23,6 @@ FixStyle(BOND_HISTORY,FixBondHistory);
 #include "fix.h"
 
 #include <map>
-#include <utility>
-#include <vector>
 
 namespace LAMMPS_NS {
 
diff --git a/src/fix_nve_noforce.cpp b/src/fix_nve_noforce.cpp
index aaac45adb0..27fcc49f13 100644
--- a/src/fix_nve_noforce.cpp
+++ b/src/fix_nve_noforce.cpp
@@ -14,7 +14,6 @@
 #include "fix_nve_noforce.h"
 
 #include "atom.h"
-#include "error.h"
 #include "respa.h"
 #include "update.h"
 
diff --git a/src/fix_pair.cpp b/src/fix_pair.cpp
index 360cee2d5a..5e5ccbf810 100644
--- a/src/fix_pair.cpp
+++ b/src/fix_pair.cpp
@@ -15,19 +15,12 @@
 #include "fix_pair.h"
 
 #include "atom.h"
-#include "dump.h"
 #include "error.h"
 #include "force.h"
 #include "fix.h"
-#include "input.h"
 #include "memory.h"
 #include "pair.h"
-#include "output.h"
-#include "variable.h"
 #include "update.h"
-#include "variable.h"
-
-#include <cstring>
 
 using namespace LAMMPS_NS;
 using namespace FixConst;
diff --git a/src/fix_store_global.cpp b/src/fix_store_global.cpp
index 0d71deb1fa..cebf4f7690 100644
--- a/src/fix_store_global.cpp
+++ b/src/fix_store_global.cpp
@@ -13,7 +13,6 @@
 
 #include "fix_store_global.h"
 
-#include "atom.h"
 #include "comm.h"
 #include "error.h"
 #include "memory.h"
diff --git a/src/fix_store_local.cpp b/src/fix_store_local.cpp
index 74083257d0..d32f0e8178 100644
--- a/src/fix_store_local.cpp
+++ b/src/fix_store_local.cpp
@@ -14,7 +14,6 @@
 #include "fix_store_local.h"
 
 #include "atom.h"
-#include "comm.h"
 #include "error.h"
 #include "memory.h"
 #include "update.h"
diff --git a/src/fix_store_peratom.cpp b/src/fix_store_peratom.cpp
index d11cb7d8c1..6f5637e3f6 100644
--- a/src/fix_store_peratom.cpp
+++ b/src/fix_store_peratom.cpp
@@ -14,7 +14,6 @@
 #include "fix_store_peratom.h"
 
 #include "atom.h"
-#include "comm.h"
 #include "error.h"
 #include "memory.h"
 
diff --git a/src/fix_update_special_bonds.h b/src/fix_update_special_bonds.h
index 722d8f5369..b211cbec64 100644
--- a/src/fix_update_special_bonds.h
+++ b/src/fix_update_special_bonds.h
@@ -23,7 +23,6 @@ FixStyle(UPDATE_SPECIAL_BONDS,FixUpdateSpecialBonds);
 #include "fix.h"
 
 #include <utility>
-#include <vector>
 
 namespace LAMMPS_NS {
 
diff --git a/src/imbalance_neigh.cpp b/src/imbalance_neigh.cpp
index ade49dd8e4..40b7f6b249 100644
--- a/src/imbalance_neigh.cpp
+++ b/src/imbalance_neigh.cpp
@@ -17,8 +17,6 @@
 #include "atom.h"
 #include "comm.h"
 #include "error.h"
-#include "neigh_list.h"
-#include "neigh_request.h"
 #include "neighbor.h"
 
 using namespace LAMMPS_NS;
diff --git a/src/improper_hybrid.cpp b/src/improper_hybrid.cpp
index b78e1ab5ca..9aa20d236e 100644
--- a/src/improper_hybrid.cpp
+++ b/src/improper_hybrid.cpp
@@ -20,7 +20,6 @@
 #include "memory.h"
 #include "neighbor.h"
 
-#include <cctype>
 #include <cstring>
 
 using namespace LAMMPS_NS;
diff --git a/src/label_map.cpp b/src/label_map.cpp
index e1cde7cae4..67b1ae480d 100644
--- a/src/label_map.cpp
+++ b/src/label_map.cpp
@@ -17,7 +17,6 @@
 #include "comm.h"
 #include "error.h"
 #include "force.h"
-#include "memory.h"
 
 #include <cstring>
 
diff --git a/src/modify.h b/src/modify.h
index 994f8ad724..b508022461 100644
--- a/src/modify.h
+++ b/src/modify.h
@@ -17,7 +17,6 @@
 #include "pointers.h"
 
 #include <map>
-#include <vector>
 
 namespace LAMMPS_NS {
 
diff --git a/src/pointers.h b/src/pointers.h
index 494daa8ffb..09efa49cbc 100644
--- a/src/pointers.h
+++ b/src/pointers.h
@@ -28,6 +28,7 @@
 #include <cstddef>      // IWYU pragme: export
 #include <cstdio>       // IWYU pragma: export
 #include <string>       // IWYU pragma: export
+#include <vector>       // IWYU pragma: export
 
 #include "fmt/format.h" // IWYU pragma: export
 #include "lammps.h"     // IWYU pragma: export