diff --git a/changes.rst b/changes.rst
index 734e2fb71..596cbc5f5 100644
--- a/changes.rst
+++ b/changes.rst
@@ -17,6 +17,7 @@ Bug fixes:
    booleans.
 -  Fix memory leak in overflow handler.
 -  Fix crash when calling ``outputJSON`` (:bugref:`856`).
+-  Fix incorrect typing of arrays in assignment generators (:bugref:`858`).
 
 .. _v2.8.7:
 
diff --git a/lib/typecheck.cpp b/lib/typecheck.cpp
index c4a128a07..2280b7137 100644
--- a/lib/typecheck.cpp
+++ b/lib/typecheck.cpp
@@ -2351,6 +2351,16 @@ class Typer {
       const Type& ty_where = Expression::type(c->where(gen_i));
       c->decl(gen_i, 0)->type(ty_where);
       c->decl(gen_i, 0)->ti()->type(ty_where);
+      if (ty_where.structBT()) {
+        c->decl(gen_i, 0)->ti()->setStructDomain(_env, ty_where);
+      } else if (ty_where.dim() > 0) {
+        GCLock lock;
+        std::vector<TypeInst*> ranges(ty_where.dim());
+        for (int i = 0; i < ty_where.dim(); i++) {
+          ranges[i] = new TypeInst(Location().introduce(), Type::parint());
+        }
+        c->decl(gen_i, 0)->ti()->setRanges(ranges);
+      }
     } else {
       const Type& ty_in = Expression::type(g_in);
       if (ty_in != Type::varsetint() && ty_in != Type::parsetint() && ty_in.dim() == 0) {
diff --git a/tests/spec/unit/regression/github_858.mzn b/tests/spec/unit/regression/github_858.mzn
new file mode 100644
index 000000000..bffa1b7bd
--- /dev/null
+++ b/tests/spec/unit/regression/github_858.mzn
@@ -0,0 +1,16 @@
+/***
+!Test
+solvers: [gecode]
+expected: !Result
+  solution: !Solution
+    _output_item: "[1][1][1]\n"
+***/
+
+array[int, int] of int: foos = [| 1, 0 |];
+
+output [
+  show([ r[1] | t=foos, i in index_set_1of2(t), r=t[i, ..] ]), % error
+  show([ r[1] | i in index_set_1of2(foos), t=foos, r=t[i, ..] ]), % error
+  show([ r[1] | i in 1..1, t=foos, r=t[i, ..] ]), % error
+  "\n",
+];