diff --git a/src/fix_ave_time.cpp b/src/fix_ave_time.cpp
index 908a21f748..5219a4de3d 100644
--- a/src/fix_ave_time.cpp
+++ b/src/fix_ave_time.cpp
@@ -1046,30 +1046,31 @@ void FixAveTime::options(int iarg, int narg, char **arg)
       }
       iarg += 2;
     } else if (strcmp(arg[iarg],"ave") == 0) {
-      if (iarg+2 > narg) error->all(FLERR,"Illegal fix ave/time command");
+      if (iarg+2 > narg) utils::missing_cmd_args(FLERR, "fix ave/time ave", error);
       if (strcmp(arg[iarg+1],"one") == 0) ave = ONE;
       else if (strcmp(arg[iarg+1],"running") == 0) ave = RUNNING;
       else if (strcmp(arg[iarg+1],"window") == 0) ave = WINDOW;
-      else error->all(FLERR,"Illegal fix ave/time command");
+      else error->all(FLERR,"Unknown fix ave/time ave keyword {}", arg[iarg+1]);
       if (ave == WINDOW) {
-        if (iarg+3 > narg) error->all(FLERR,"Illegal fix ave/time command");
+        if (iarg+3 > narg) utils::missing_cmd_args(FLERR, "fix ave/time ave window", error);
         nwindow = utils::inumeric(FLERR,arg[iarg+2],false,lmp);
-        if (nwindow <= 0) error->all(FLERR,"Illegal fix ave/time command");
+        if (nwindow <= 0)
+          error->all(FLERR,"Illegal fix ave/time ave window argument {}; must be > 0", nwindow);
       }
       iarg += 2;
       if (ave == WINDOW) iarg++;
     } else if (strcmp(arg[iarg],"start") == 0) {
-      if (iarg+2 > narg) error->all(FLERR,"Illegal fix ave/time command");
+      if (iarg+2 > narg) utils::missing_cmd_args(FLERR, "fix ave/time start", error);
       startstep = utils::inumeric(FLERR,arg[iarg+1],false,lmp);
       iarg += 2;
     } else if (strcmp(arg[iarg],"mode") == 0) {
-      if (iarg+2 > narg) error->all(FLERR,"Illegal fix ave/time command");
+      if (iarg+2 > narg) utils::missing_cmd_args(FLERR, "fix ave/time mode", error);
       if (strcmp(arg[iarg+1],"scalar") == 0) mode = SCALAR;
       else if (strcmp(arg[iarg+1],"vector") == 0) mode = VECTOR;
-      else error->all(FLERR,"Illegal fix ave/time command");
+      else error->all(FLERR,"Unknown fix ave/time mode {}", arg[iarg+1]);
       iarg += 2;
     } else if (strcmp(arg[iarg],"off") == 0) {
-      if (iarg+2 > narg) error->all(FLERR,"Illegal fix ave/time command");
+      if (iarg+2 > narg) utils::missing_cmd_args(FLERR, "fix ave/time off", error);
       memory->grow(offlist,noff+1,"ave/time:offlist");
       offlist[noff++] = utils::inumeric(FLERR,arg[iarg+1],false,lmp);
       iarg += 2;
@@ -1077,27 +1078,27 @@ void FixAveTime::options(int iarg, int narg, char **arg)
       overwrite = 1;
       iarg += 1;
     } else if (strcmp(arg[iarg],"format") == 0) {
-      if (iarg+2 > narg) error->all(FLERR,"Illegal fix ave/time command");
+      if (iarg+2 > narg) utils::missing_cmd_args(FLERR, "fix ave/time format", error);
       delete[] format_user;
       format_user = utils::strdup(arg[iarg+1]);
       format = format_user;
       iarg += 2;
     } else if (strcmp(arg[iarg],"title1") == 0) {
-      if (iarg+2 > narg) error->all(FLERR,"Illegal fix ave/time command");
+      if (iarg+2 > narg) utils::missing_cmd_args(FLERR, "fix ave/time title1", error);
       delete[] title1;
       title1 = utils::strdup(arg[iarg+1]);
       iarg += 2;
     } else if (strcmp(arg[iarg],"title2") == 0) {
-      if (iarg+2 > narg) error->all(FLERR,"Illegal fix ave/time command");
+      if (iarg+2 > narg) utils::missing_cmd_args(FLERR, "fix ave/time title2", error);
       delete[] title2;
       title2 = utils::strdup(arg[iarg+1]);
       iarg += 2;
     } else if (strcmp(arg[iarg],"title3") == 0) {
-      if (iarg+2 > narg) error->all(FLERR,"Illegal fix ave/time command");
+      if (iarg+2 > narg) utils::missing_cmd_args(FLERR, "fix ave/time title3", error);
       delete[] title3;
       title3 = utils::strdup(arg[iarg+1]);
       iarg += 2;
-    } else error->all(FLERR,"Unknown fix ave/time command option {}", arg[iarg]);
+    } else error->all(FLERR,"Unknown fix ave/time keyword {}", arg[iarg]);
   }
 }