diff --git a/src/compute_chunk_spread_atom.cpp b/src/compute_chunk_spread_atom.cpp
index 933cf0af0c..53b8517c22 100644
--- a/src/compute_chunk_spread_atom.cpp
+++ b/src/compute_chunk_spread_atom.cpp
@@ -106,7 +106,7 @@ ComputeChunkSpreadAtom(LAMMPS *lmp, int narg, char **arg) :
 
     } else if (val.which == ArgInfo::FIX) {
       auto ifix = modify->get_fix_by_id(val.id);
-      if (ifix)
+      if (!ifix)
         error->all(FLERR,"Fix ID {} for compute chunk/spread/atom does not exist", val.id);
       if (val.argindex == 0) {
         if (!ifix->vector_flag)
diff --git a/src/fix_press_berendsen.cpp b/src/fix_press_berendsen.cpp
index da49b3dbdb..e27a4560f0 100644
--- a/src/fix_press_berendsen.cpp
+++ b/src/fix_press_berendsen.cpp
@@ -491,7 +491,7 @@ int FixPressBerendsen::modify_param(int narg, char **arg)
     id_press = utils::strdup(arg[1]);
 
     pressure = modify->get_compute_by_id(arg[1]);
-    if (pressure) error->all(FLERR,"Could not find fix_modify pressure compute ID: {}", arg[1]);
+    if (!pressure) error->all(FLERR,"Could not find fix_modify pressure compute ID: {}", arg[1]);
     if (pressure->pressflag == 0)
       error->all(FLERR,"Fix_modify pressure compute {} does not compute pressure", arg[1]);
     return 2;