diff --git a/NEWS b/NEWS
index 569bcdab4..487c048eb 100644
--- a/NEWS
+++ b/NEWS
@@ -23,6 +23,8 @@ Any uppercase BUG_* names are modernish shell bug IDs.
   of declaration built-ins. This reverts a change introduced on 2020-09-11.
   [*] https://austingroupbugs.net/view.php?id=1393
 
+- Fixed arithmetic assignment operations for multidimensional indexed arrays
+
 2021-04-30:
 
 - The emacs 'ESC .' (M-.) and vi '_' commands now take shell quoting into
diff --git a/src/cmd/ksh93/include/streval.h b/src/cmd/ksh93/include/streval.h
index ea64a0c8b..a62cc6b9f 100644
--- a/src/cmd/ksh93/include/streval.h
+++ b/src/cmd/ksh93/include/streval.h
@@ -76,6 +76,7 @@ struct lval
 	const char	*expr;
 	const  void	*ptr;
 	int		nosub;
+	char		*sub;
 	short		flag;
 	short		nargs;
 	short		emode;
diff --git a/src/cmd/ksh93/sh/arith.c b/src/cmd/ksh93/sh/arith.c
index 47de20723..603876c06 100644
--- a/src/cmd/ksh93/sh/arith.c
+++ b/src/cmd/ksh93/sh/arith.c
@@ -233,8 +233,17 @@ static Sfdouble_t arith(const char **ptr, struct lval *lvalue, int type, Sfdoubl
 	{
 	    case ASSIGN:
 	    {
-		register Namval_t *np = (Namval_t*)(lvalue->value);
-		np = scope(np,lvalue,1);
+		register Namval_t *np;
+		if (lvalue->nosub > 0 && lvalue->sub) /* indexed array ARITH_ASSIGNOP */
+		{
+			np = (Namval_t*)lvalue->sub; /* use saved subscript reference instead of last worked value */
+			nv_putsub(np, NIL(char*), lvalue->nosub-1);
+		}
+		else
+		{
+			np = (Namval_t*)lvalue->value;
+			np = scope(np, lvalue, 1);
+		}
 		nv_putval(np, (char*)&n, NV_LDOUBLE);
 		if(lvalue->eflag)
 			lvalue->ptr = (void*)nv_hasdisc(np,&ENUM_disc);
@@ -494,7 +503,10 @@ static Sfdouble_t arith(const char **ptr, struct lval *lvalue, int type, Sfdoubl
 		else if(nv_isattr(np,NV_DOUBLE)==NV_DOUBLE)
 			lvalue->isfloat=1;
 		if((lvalue->emode&ARITH_ASSIGNOP) && nv_isarray(np))
-			lvalue->nosub = nv_aindex(np)+1;
+		{
+			lvalue->nosub = nv_aindex(np)+1; /* subscript number of array */
+			lvalue->sub = (char*)np; /* store subscript reference for upcoming iteration of ASSIGN */
+		}
 		return(r);
 	    }
 
diff --git a/src/cmd/ksh93/sh/streval.c b/src/cmd/ksh93/sh/streval.c
index a115ee9f3..98e449ec9 100644
--- a/src/cmd/ksh93/sh/streval.c
+++ b/src/cmd/ksh93/sh/streval.c
@@ -172,6 +172,7 @@ Sfdouble_t	arith_exec(Arith_t *ep)
 	node.elen = ep->elen;
 	node.value = 0;
 	node.nosub = 0;
+	node.sub = 0;
 	node.ptr = 0;
 	node.eflag = 0;
 	if(shp->arithrecursion++ >= MAXLEVEL)
diff --git a/src/cmd/ksh93/tests/arrays2.sh b/src/cmd/ksh93/tests/arrays2.sh
index 5771a1d5c..2f7fda3bd 100755
--- a/src/cmd/ksh93/tests/arrays2.sh
+++ b/src/cmd/ksh93/tests/arrays2.sh
@@ -240,5 +240,24 @@ foo
 EOF
 $SHELL "$multiarray_unset" > /dev/null || err_exit 'Multidimensional arrays with an unset method crash ksh'
 
+# ======
+# Multidimensional indexed array arithmetic assignment operation tests
+ini() { unset arr; typeset -a arr=((10 20) 6 8); }
+[[ $( ini; ((arr[0][0]+=1)); typeset -p arr) == 'typeset -a arr=((11 20) 6 8)' ]] || err_exit 'ASSIGNOP: arr[0][0]+=1 failed.'
+[[ $( ini; ((arr[0][1]+=1)); typeset -p arr) == 'typeset -a arr=((10 21) 6 8)' ]] || err_exit 'ASSIGNOP: arr[0][1]+=1 failed.'
+[[ $( ini; ((arr[0][2]+=1)); typeset -p arr) == 'typeset -a arr=((10 20 1) 6 8)' ]] || err_exit 'ASSIGNOP: arr[0][2]+=1 failed.'
+[[ $( ini; ((arr[0][1]+=arr[1])); typeset -p arr) == 'typeset -a arr=((10 26) 6 8)' ]] || err_exit 'ASSIGNOP: arr[0][1]+=arr[1] failed.'
+[[ $( ini; ((arr[0][2]+=arr[1])); typeset -p arr) == 'typeset -a arr=((10 20 6) 6 8)' ]] || err_exit 'ASSIGNOP: arr[0][2]+=arr[1] failed.'
+[[ $( ini; ((arr[1]+=1)); typeset -p arr) == 'typeset -a arr=((10 20) 7 8)' ]] || err_exit 'ASSIGNOP: arr[1]+=1 failed.'
+[[ $( ini; ((arr[2]+=1)); typeset -p arr) == 'typeset -a arr=((10 20) 6 9)' ]] || err_exit 'ASSIGNOP: arr[2]+=1 failed.'
+[[ $( ini; ((arr[3]+=1)); typeset -p arr) == 'typeset -a arr=((10 20) 6 8 1)' ]] || err_exit 'ASSIGNOP: arr[3]+=1 failed.'
+[[ $( ini; ((arr[1]+=arr[0][0])); typeset -p arr) == 'typeset -a arr=((10 20) 16 8)' ]] || err_exit 'ASSIGNOP: arr[1]+=arr[0][0] failed.'
+[[ $( ini; ((arr[1]+=arr[0][1])); typeset -p arr) == 'typeset -a arr=((10 20) 26 8)' ]] || err_exit 'ASSIGNOP: arr[1]+=arr[0][1] failed.'
+[[ $( ini; ((arr[2]+=arr[0][0])); typeset -p arr) == 'typeset -a arr=((10 20) 6 18)' ]] || err_exit 'ASSIGNOP: arr[2]+=arr[0][0] failed.'
+[[ $( ini; ((arr[2]+=arr[0][1])); typeset -p arr) == 'typeset -a arr=((10 20) 6 28)' ]] || err_exit 'ASSIGNOP: arr[2]+=arr[0][1] failed.'
+[[ $( ini; ((arr[3]+=arr[0][1])); typeset -p arr) == 'typeset -a arr=((10 20) 6 8 20)' ]] || err_exit 'ASSIGNOP: arr[2]+=arr[0][1] failed.'
+unset arr
+unset -f ini
+
 # ======
 exit $((Errors<125?Errors:125))