diff --git a/src/fix_nve.cpp b/src/fix_nve.cpp
index 728036128a..a4c9060e6a 100644
--- a/src/fix_nve.cpp
+++ b/src/fix_nve.cpp
@@ -29,7 +29,7 @@ FixNVE::FixNVE(LAMMPS *lmp, int narg, char **arg) :
   Fix(lmp, narg, arg)
 {
   if (!utils::strmatch(style,"^nve/sphere") && narg < 3)
-    error->all(FLERR,"Illegal fix nve command");
+    utils::missing_cmd_args(FLERR, "fix nve", error);
 
   dynamic_group_allow = 1;
   time_integrate = 1;
diff --git a/src/fix_nve_limit.cpp b/src/fix_nve_limit.cpp
index cb6d7c7302..fdebcf5bfe 100644
--- a/src/fix_nve_limit.cpp
+++ b/src/fix_nve_limit.cpp
@@ -32,7 +32,7 @@ using namespace FixConst;
 FixNVELimit::FixNVELimit(LAMMPS *lmp, int narg, char **arg) :
   Fix(lmp, narg, arg)
 {
-  if (narg != 4) error->all(FLERR,"Illegal fix nve/limit command");
+  if (narg != 4) utils::missing_cmd_args(FLERR, "fix nve/limit", error);
 
   time_integrate = 1;
   scalar_flag = 1;
diff --git a/src/fix_nve_noforce.cpp b/src/fix_nve_noforce.cpp
index 7b79dcc267..9124dfac3e 100644
--- a/src/fix_nve_noforce.cpp
+++ b/src/fix_nve_noforce.cpp
@@ -25,7 +25,7 @@ using namespace FixConst;
 
 FixNVENoforce::FixNVENoforce(LAMMPS *lmp, int narg, char **arg) : Fix(lmp, narg, arg)
 {
-  if (narg != 3) error->all(FLERR, "Illegal fix nve/noforce command");
+  if (narg != 3) utils::missing_cmd_args(FLERR, "fix nve/noforce", error);
 
   time_integrate = 1;
 }
diff --git a/src/fix_nve_sphere.cpp b/src/fix_nve_sphere.cpp
index 5cc9167ed5..8ece78d011 100644
--- a/src/fix_nve_sphere.cpp
+++ b/src/fix_nve_sphere.cpp
@@ -35,7 +35,7 @@ enum{NODLM,DLM};
 FixNVESphere::FixNVESphere(LAMMPS *lmp, int narg, char **arg) :
   FixNVE(lmp, narg, arg)
 {
-  if (narg < 3) error->all(FLERR,"Illegal fix nve/sphere command");
+  if (narg < 3) utils::missing_cmd_args(FLERR, "fix nve/sphere", error);
 
   time_integrate = 1;
 
@@ -49,12 +49,12 @@ FixNVESphere::FixNVESphere(LAMMPS *lmp, int narg, char **arg) :
   int iarg = 3;
   while (iarg < narg) {
     if (strcmp(arg[iarg],"update") == 0) {
-      if (iarg+2 > narg) error->all(FLERR,"Illegal fix nve/sphere command");
+      if (iarg+2 > narg) utils::missing_cmd_args(FLERR, "fix nve/sphere update", error);
       if (strcmp(arg[iarg+1],"dipole") == 0) extra = DIPOLE;
       else if (strcmp(arg[iarg+1],"dipole/dlm") == 0) {
         extra = DIPOLE;
         dlm = DLM;
-      } else error->all(FLERR,"Illegal fix nve/sphere command");
+      } else error->all(FLERR,"Unknown keyword in fix nve/sphere update command: {}",arg[iarg+1]);
       iarg += 2;
     }
     else if (strcmp(arg[iarg],"disc")==0) {
@@ -63,7 +63,7 @@ FixNVESphere::FixNVESphere(LAMMPS *lmp, int narg, char **arg) :
         error->all(FLERR,"Fix nve/sphere disc requires 2d simulation");
       iarg++;
     }
-    else error->all(FLERR,"Illegal fix nve/sphere command");
+    else error->all(FLERR,"Unknown keyword in fix nve/sphere command: {}",arg[iarg]);
   }
 
   // error checks