diff --git a/src/cmd/ksh93/sh/name.c b/src/cmd/ksh93/sh/name.c
index ae3f582d8..e4dec7d5a 100644
--- a/src/cmd/ksh93/sh/name.c
+++ b/src/cmd/ksh93/sh/name.c
@@ -261,6 +261,7 @@ void nv_setlist(register struct argnod *arg,register int flags, Namval_t *typ)
 	Shell_t		*shp = sh_getinterp();
 	register char	*cp;
 	register Namval_t *np, *mp;
+	char		*eqp;
 	char		*trap=shp->st.trap[SH_DEBUGTRAP];
 	char		*prefix = shp->prefix;
 	int		traceon = (sh_isoption(SH_XTRACE)!=0);
@@ -592,6 +593,19 @@ void nv_setlist(register struct argnod *arg,register int flags, Namval_t *typ)
 			cp = arg->argval;
 			mp = 0;
 		}
+		if(eqp = strchr(cp,'='))
+		{
+			/* Check for read-only */
+			*eqp = '\0';
+			np = nv_search(cp,shp->var_tree,0);
+			*eqp = '=';
+			if(np && nv_isattr(np,NV_RDONLY))
+			{
+				errormsg(SH_DICT,ERROR_exit(1),e_readonly,nv_name(np));
+				UNREACHABLE();
+			}
+
+		}
 		np = nv_open(cp,shp->prefix_root?shp->prefix_root:shp->var_tree,flags);
 		if(!np->nvfun && (flags&NV_NOREF))
 		{
diff --git a/src/cmd/ksh93/tests/readonly.sh b/src/cmd/ksh93/tests/readonly.sh
index 778c54090..64b35f5e2 100755
--- a/src/cmd/ksh93/tests/readonly.sh
+++ b/src/cmd/ksh93/tests/readonly.sh
@@ -319,6 +319,7 @@ n=${#rtests[@]}
 for ((i=0; i<$n; i++))
 do
 	got=$(
+		((.sh.version < 20210404)) && ulimit -t unlimited 2>/dev/null	# fork to dodge an arith recursion detection bug
 		trap "${rtests[$i].res}" EXIT
 		eval "${rtests[$i].ini}"
 		eval "${rtests[$i].chg}" 2>&1
@@ -340,5 +341,9 @@ unset i n got rtests
 (readonly v=1; typeset -x v) 2>/dev/null || err_exit "readonly variable cannot be exported (2)"
 (readonly v=1; typeset -rx v) 2>/dev/null || err_exit "readonly variable cannot be set readonly and exported"
 
+# ======
+# the environment list was not checked for readonly for commands that are not fork()ed
+(readonly v=1; v=2 true) 2>/dev/null && err_exit 'readonly not verified for command environment list'
+
 # ======
 exit $((Errors<125?Errors:125))