diff --git a/src/cmd/gc/go.h b/src/cmd/gc/go.h
index 46be44d5ee..9b4ab47312 100644
--- a/src/cmd/gc/go.h
+++ b/src/cmd/gc/go.h
@@ -348,7 +348,6 @@ enum
 	OADD, OSUB, OOR, OXOR, OADDSTR,
 	OADDR,
 	OANDAND,
-	OAPPENDSTR,
 	OARRAY,
 	OARRAYBYTESTR, OARRAYRUNESTR,
 	OSTRARRAYBYTE, OSTRARRAYRUNE,
@@ -1066,7 +1065,6 @@ Node*	ascompatee1(int, Node*, Node*, NodeList**);
 NodeList*	ascompatee(int, NodeList*, NodeList*, NodeList**);
 NodeList*	ascompatet(int, NodeList*, Type**, int, NodeList**);
 NodeList*	ascompatte(int, Type**, NodeList*, int, NodeList**);
-Node*	mapop(Node*, NodeList**);
 Type*	fixchan(Type*);
 Node*	ifacecvt(Type*, Node*, int, NodeList**);
 int	ifaceas(Type*, Type*, int);
diff --git a/src/cmd/gc/typecheck.c b/src/cmd/gc/typecheck.c
index 4e5b5bbcd5..a7ea631e1c 100644
--- a/src/cmd/gc/typecheck.c
+++ b/src/cmd/gc/typecheck.c
@@ -80,8 +80,10 @@ typecheck(Node **np, int top)
 		}
 	}
 
-	if(n->typecheck == 2)
-		fatal("typecheck loop");
+	if(n->typecheck == 2) {
+		yyerror("typechecking loop");
+		return n;
+	}
 	n->typecheck = 2;
 
 redo:
@@ -355,9 +357,7 @@ reswitch:
 			if(iscmp[n->op]) {
 				n->etype = n->op;
 				n->op = OCMPSTR;
-			} else if(n->op == OASOP)
-				n->op = OAPPENDSTR;
-			else if(n->op == OADD)
+			} else if(n->op == OADD)
 				n->op = OADDSTR;
 		}
 		if(et == TINTER) {
diff --git a/src/cmd/gc/walk.c b/src/cmd/gc/walk.c
index 65ab491f6f..3820a58ff3 100644
--- a/src/cmd/gc/walk.c
+++ b/src/cmd/gc/walk.c
@@ -354,7 +354,6 @@ walkstmt(Node **np)
 		dump("nottop", n);
 		break;
 
-	case OAPPENDSTR:
 	case OASOP:
 	case OAS:
 	case OAS2:
@@ -522,8 +521,8 @@ walkexprlistsafe(NodeList *l, NodeList **init)
 void
 walkexpr(Node **np, NodeList **init)
 {
-	Node *r, *l;
-	NodeList *ll, *lr;
+	Node *r, *l, *var, *a;
+	NodeList *ll, *lr, *lpost;
 	Type *t;
 	int et;
 	int32 lno;
@@ -707,8 +706,35 @@ walkexpr(Node **np, NodeList **init)
 		r = n->rlist->n;
 		walkexprlistsafe(n->list, init);
 		walkexpr(&r, init);
+		l = n->list->n;
+		
+		// all the really hard stuff - explicit function calls and so on -
+		// is gone, but map assignments remain.
+		// if there are map assignments here, assign via
+		// temporaries, because ascompatet assumes
+		// the targets can be addressed without function calls
+		// and map index has an implicit one.
+		lpost = nil;
+		if(l->op == OINDEXMAP) {
+			var = nod(OXXX, N, N);
+			tempname(var, l->type);
+			n->list->n = var;
+			a = nod(OAS, l, var);
+			typecheck(&a, Etop);
+			lpost = list(lpost, a);
+		}
+		l = n->list->next->n;
+		if(l->op == OINDEXMAP) {
+			var = nod(OXXX, N, N);
+			tempname(var, l->type);
+			n->list->next->n = var;
+			a = nod(OAS, l, var);
+			typecheck(&a, Etop);
+			lpost = list(lpost, a);
+		}
 		ll = ascompatet(n->op, n->list, &r->type, 0, init);
-		n = liststmt(concat(list1(r), ll));
+		walkexprlist(lpost, init);
+		n = liststmt(concat(concat(list1(r), ll), lpost));
 		goto ret;
 
 	case OAS2RECV:
@@ -815,26 +841,35 @@ walkexpr(Node **np, NodeList **init)
 		n->left = safeexpr(n->left, init);
 		walkexpr(&n->left, init);
 		l = n->left;
-		if(l->op == OINDEXMAP)
-			n = mapop(n, init);
 		walkexpr(&n->right, init);
 		if(n->etype == OANDNOT) {
 			n->etype = OAND;
 			n->right = nod(OCOM, n->right, N);
 			typecheck(&n->right, Erv);
-			goto ret;
 		}
 
 		/*
 		 * on 32-bit arch, rewrite 64-bit ops into l = l op r.
 		 * on 386, rewrite float ops into l = l op r.
+		 * everywhere, rewrite map ops into l = l op r.
+		 * everywhere, rewrite string += into l = l op r.
 		 * TODO(rsc): Maybe this rewrite should be done always?
 		 */
 		et = n->left->type->etype;
 		if((widthptr == 4 && (et == TUINT64 || et == TINT64)) ||
-		   (thechar == '8' && isfloat[et])) {
+		   (thechar == '8' && isfloat[et]) ||
+		   l->op == OINDEXMAP ||
+		   et == TSTRING) {
 			l = safeexpr(n->left, init);
-			r = nod(OAS, l, nod(n->etype, l, n->right));
+			a = l;
+			if(a->op == OINDEXMAP) {
+				// map index has "lhs" bit set in a->etype.
+				// make a copy so we can clear it on the rhs.
+				a = nod(OXXX, N, N);
+				*a = *l;
+				a->etype = 0;
+			}
+			r = nod(OAS, l, nod(n->etype, a, n->right));
 			typecheck(&r, Etop);
 			walkexpr(&r, init);
 			n = r;
@@ -1016,17 +1051,6 @@ walkexpr(Node **np, NodeList **init)
 			conv(n->right, types[TSTRING]));
 		goto ret;
 
-	case OAPPENDSTR:
-		// s1 = sys_catstring(s1, s2)
-		if(n->etype != OADD)
-			fatal("walkasopstring: not add");
-		r = mkcall("catstring", n->left->type, init,
-			conv(n->left, types[TSTRING]),
-			conv(n->right, types[TSTRING]));
-		r = nod(OAS, n->left, r);
-		n = r;
-		goto ret;
-
 	case OSLICESTR:
 		// sys_slicestring(s, lb, hb)
 		if(n->right->right) {
@@ -1366,7 +1390,7 @@ ascompatet(int op, NodeList *nl, Type **nr, int fp, NodeList **init)
 		yyerror("assignment count mismatch: %d = %d",
 			count(nl), structcount(*nr));
 	if(ucount)
-		yyerror("reorder2: too many function calls evaluating parameters");
+		fatal("reorder2: too many function calls evaluating parameters");
 	return concat(nn, mm);
 }
 
@@ -1862,35 +1886,6 @@ bad:
 	return T;
 }
 
-Node*
-mapop(Node *n, NodeList **init)
-{
-	Node *r, *a;
-
-	r = n;
-	switch(n->op) {
-	default:
-		fatal("mapop: unknown op %O", n->op);
-	case OASOP:
-		// rewrite map[index] op= right
-		// into tmpi := index; map[tmpi] = map[tmpi] op right
-
-		// make it ok to double-evaluate map[tmpi]
-		n->left->left = safeexpr(n->left->left, init);
-		n->left->right = safeexpr(n->left->right, init);
-
-		a = nod(OXXX, N, N);
-		*a = *n->left;		// copy of map[tmpi]
-		a->etype = 0;
-		a = nod(n->etype, a, n->right);		// m[tmpi] op right
-		r = nod(OAS, n->left, a);		// map[tmpi] = map[tmpi] op right
-		typecheck(&r, Etop);
-		walkexpr(&r, init);
-		break;
-	}
-	return r;
-}
-
 /*
  * assigning src to dst involving interfaces?
  * return op to use.
diff --git a/test/golden.out b/test/golden.out
index 96ab549438..036519de70 100644
--- a/test/golden.out
+++ b/test/golden.out
@@ -159,7 +159,7 @@ do break
 broke
 
 =========== fixedbugs/bug081.go
-fixedbugs/bug081.go:9: fatal error: typecheck loop
+fixedbugs/bug081.go:9: typechecking loop
 
 =========== fixedbugs/bug093.go
 M