diff -r ce3b22951c7e Lib/test/test_ast.py
--- a/Lib/test/test_ast.py	Fri Nov 23 22:17:02 2012 +0200
+++ b/Lib/test/test_ast.py	Sat Nov 24 18:10:09 2012 +0000
@@ -840,6 +840,11 @@
         self.expr(ast.Yield(ast.Name("x", ast.Store())), "must have Load")
         self.expr(ast.YieldFrom(ast.Name("x", ast.Store())), "must have Load")
 
+        # Issue 16546: yield from value is not optional.
+        empty_yield_from = ast.parse("def f():\n yield from g()")
+        empty_yield_from.body[0].body[0].value.value = None
+        self.mod(empty_yield_from, "field value is required")
+
     def test_compare(self):
         left = ast.Name("x", ast.Load())
         comp = ast.Compare(left, [ast.In()], [])
diff -r ce3b22951c7e Parser/Python.asdl
--- a/Parser/Python.asdl	Fri Nov 23 22:17:02 2012 +0200
+++ b/Parser/Python.asdl	Sat Nov 24 18:10:09 2012 +0000
@@ -60,7 +60,7 @@
          | GeneratorExp(expr elt, comprehension* generators)
          -- the grammar constrains where yield expressions can occur
          | Yield(expr? value)
-             | YieldFrom(expr? value)
+         | YieldFrom(expr value)
          -- need sequences for compare to distinguish between
          -- x < 4 < 3 and (x < 4) < 3
          | Compare(expr left, cmpop* ops, expr* comparators)
diff -r ce3b22951c7e Python/Python-ast.c
--- a/Python/Python-ast.c	Fri Nov 23 22:17:02 2012 +0200
+++ b/Python/Python-ast.c	Sat Nov 24 18:10:09 2012 +0000
@@ -1802,6 +1802,11 @@
 YieldFrom(expr_ty value, int lineno, int col_offset, PyArena *arena)
 {
         expr_ty p;
+        if (!value) {
+                PyErr_SetString(PyExc_ValueError,
+                                "field value is required for YieldFrom");
+                return NULL;
+        }
         p = (expr_ty)PyArena_Malloc(arena, sizeof(*p));
         if (!p)
                 return NULL;
@@ -5431,7 +5436,8 @@
                         Py_XDECREF(tmp);
                         tmp = NULL;
                 } else {
-                        value = NULL;
+                        PyErr_SetString(PyExc_TypeError, "required field \"value\" missing from YieldFrom");
+                        return 1;
                 }
                 *out = YieldFrom(value, lineno, col_offset, arena);
                 if (*out == NULL) goto failed;
diff -r ce3b22951c7e Python/ast.c
--- a/Python/ast.c	Fri Nov 23 22:17:02 2012 +0200
+++ b/Python/ast.c	Sat Nov 24 18:10:09 2012 +0000
@@ -224,8 +224,7 @@
     case Yield_kind:
         return !exp->v.Yield.value || validate_expr(exp->v.Yield.value, Load);
     case YieldFrom_kind:
-        return !exp->v.YieldFrom.value ||
-            validate_expr(exp->v.YieldFrom.value, Load);
+        return validate_expr(exp->v.YieldFrom.value, Load);
     case Compare_kind:
         if (!asdl_seq_LEN(exp->v.Compare.comparators)) {
             PyErr_SetString(PyExc_ValueError, "Compare with no comparators");
diff -r ce3b22951c7e Python/compile.c
--- a/Python/compile.c	Fri Nov 23 22:17:02 2012 +0200
+++ b/Python/compile.c	Sat Nov 24 18:10:09 2012 +0000
@@ -3341,27 +3341,24 @@
     case DictComp_kind:
         return compiler_dictcomp(c, e);
     case Yield_kind:
-    case YieldFrom_kind: {
-        expr_ty value;
         if (c->u->u_ste->ste_type != FunctionBlock)
             return compiler_error(c, "'yield' outside function");
-        value = (e->kind == YieldFrom_kind) ? e->v.YieldFrom.value : e->v.Yield.value;
-        if (value) {
-            VISIT(c, expr, value);
+        if (e->v.Yield.value) {
+            VISIT(c, expr, e->v.Yield.value);
         }
         else {
             ADDOP_O(c, LOAD_CONST, Py_None, consts);
         }
-        if (e->kind == YieldFrom_kind) {
-            ADDOP(c, GET_ITER);
-            ADDOP_O(c, LOAD_CONST, Py_None, consts);
-            ADDOP(c, YIELD_FROM);
-        }
-        else {
-            ADDOP(c, YIELD_VALUE);
-        }
+        ADDOP(c, YIELD_VALUE);
         break;
-    }
+    case YieldFrom_kind:
+        if (c->u->u_ste->ste_type != FunctionBlock)
+            return compiler_error(c, "'yield' outside function");
+        VISIT(c, expr, e->v.YieldFrom.value);
+        ADDOP(c, GET_ITER);
+        ADDOP_O(c, LOAD_CONST, Py_None, consts);
+        ADDOP(c, YIELD_FROM);
+        break;
     case Compare_kind:
         return compiler_compare(c, e);
     case Call_kind:
diff -r ce3b22951c7e Python/symtable.c
--- a/Python/symtable.c	Fri Nov 23 22:17:02 2012 +0200
+++ b/Python/symtable.c	Sat Nov 24 18:10:09 2012 +0000
@@ -1412,14 +1412,14 @@
             VISIT_QUIT(st, 0);
         break;
     case Yield_kind:
-    case YieldFrom_kind: {
-        expr_ty value;
-        value = (e->kind == YieldFrom_kind) ? e->v.YieldFrom.value : e->v.Yield.value;
-        if (value)
-            VISIT(st, expr, value);
+        if (e->v.Yield.value)
+            VISIT(st, expr, e->v.Yield.value);
         st->st_cur->ste_generator = 1;
         break;
-    }
+    case YieldFrom_kind:
+        VISIT(st, expr, e->v.YieldFrom.value);
+        st->st_cur->ste_generator = 1;
+        break;
     case Compare_kind:
         VISIT(st, expr, e->v.Compare.left);
         VISIT_SEQ(st, expr, e->v.Compare.comparators);