diff --git a/src/group.cpp b/src/group.cpp
index 00677cca5a..765fe4d85d 100644
--- a/src/group.cpp
+++ b/src/group.cpp
@@ -99,6 +99,7 @@ void Group::assign(int narg, char **arg)
   // clear mask of each atom assigned to this group
 
   if (strcmp(arg[1],"delete") == 0) {
+    if (narg != 2) error->all(FLERR,"Illegal group command");
     int igroup = find(arg[0]);
     if (igroup == -1) error->all(FLERR,"Could not find group delete group ID");
     if (igroup == 0) error->all(FLERR,"Cannot delete group all");
@@ -183,7 +184,8 @@ void Group::assign(int narg, char **arg)
 
   } else if (strcmp(arg[1],"empty") == 0) {
 
-    ; // nothing to do here
+    if (narg != 2) error->all(FLERR,"Illegal group command");
+    // nothing else to do here
 
   // style = type, molecule, id
   // add to group if atom matches type/molecule/id or condition
@@ -546,7 +548,7 @@ void Group::assign(const std::string &groupcmd)
    add flagged atoms to a new or existing group
 ------------------------------------------------------------------------- */
 
-void Group::create(char *name, int *flag)
+void Group::create(const char *name, int *flag)
 {
   int i;
 
diff --git a/src/group.h b/src/group.h
index 39c446d119..0c5a18384c 100644
--- a/src/group.h
+++ b/src/group.h
@@ -32,7 +32,7 @@ class Group : protected Pointers {
   ~Group();
   void assign(int, char **);         // assign atoms to a group
   void assign(const std::string &);  // convenience function
-  void create(char *, int *);        // add flagged atoms to a group
+  void create(const char *, int *);  // add flagged atoms to a group
   int find(const std::string &);     // lookup name in list of groups
   int find_or_create(const char *);  // lookup name or create new group
   void write_restart(FILE *);