diff --git a/src/go/types/expr.go b/src/go/types/expr.go
index 1f8b946..11f9411 100644
--- a/src/go/types/expr.go
+++ b/src/go/types/expr.go
@@ -1357,9 +1357,7 @@
 			var key operand
 			check.expr(&key, e.Index)
 			check.assignment(&key, typ.key, "map index")
-			if x.mode == invalid {
-				goto Error
-			}
+			// ok to continue even if indexing failed - map element type is known
 			x.mode = mapindex
 			x.typ = typ.elem
 			x.expr = e
diff --git a/src/go/types/testdata/expr3.src b/src/go/types/testdata/expr3.src
index 6f2201c..e6777aa 100644
--- a/src/go/types/testdata/expr3.src
+++ b/src/go/types/testdata/expr3.src
@@ -102,6 +102,7 @@
 	var ok mybool
 	_, ok = m["bar"]
 	_ = ok
+	_ = m[0 /* ERROR "cannot use 0" */ ] + "foo" // ERROR "cannot convert"
 
 	var t string
 	_ = t[- /* ERROR "negative" */ 1]