diff --git a/src/USER-PTM/compute_ptm_atom.h b/src/USER-PTM/compute_ptm_atom.h
index 5c10e0c443..586d7a44cd 100644
--- a/src/USER-PTM/compute_ptm_atom.h
+++ b/src/USER-PTM/compute_ptm_atom.h
@@ -35,7 +35,7 @@ class ComputePTMAtom : public Compute {
 
  private:
   int nmax;
-  int32_t input_flags;
+  smallint input_flags;
   double rmsd_threshold;
   class NeighList *list;
   double **output;
diff --git a/src/USER-PTM/ptm_neighbour_ordering.h b/src/USER-PTM/ptm_neighbour_ordering.h
index 4a4fb8ce8b..2a619880bb 100644
--- a/src/USER-PTM/ptm_neighbour_ordering.h
+++ b/src/USER-PTM/ptm_neighbour_ordering.h
@@ -11,6 +11,7 @@ THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLI
 #define PTM_NEIGHBOUR_ORDERING_H
 
 #include <cstddef>
+#include <stdint.h>
 
 namespace ptm {