diff --git a/dlls/jscript/engine.c b/dlls/jscript/engine.c
index 9b6ace9dc2..a566f81d8a 100644
--- a/dlls/jscript/engine.c
+++ b/dlls/jscript/engine.c
@@ -2080,10 +2080,14 @@ HRESULT assign_add_expression_eval(exec_ctx_t *ctx, expression_t *_expr, DWORD f
     return assign_oper_eval(ctx, expr->expression1, expr->expression2, add_eval, ei, ret);
 }
 
-HRESULT assign_sub_expression_eval(exec_ctx_t *ctx, expression_t *expr, DWORD flags, jsexcept_t *ei, exprval_t *ret)
+/* ECMA-262 3rd Edition    11.13.2 */
+HRESULT assign_sub_expression_eval(exec_ctx_t *ctx, expression_t *_expr, DWORD flags, jsexcept_t *ei, exprval_t *ret)
 {
-    FIXME("\n");
-    return E_NOTIMPL;
+    binary_expression_t *expr = (binary_expression_t*)_expr;
+
+    TRACE("\n");
+
+    return assign_oper_eval(ctx, expr->expression1, expr->expression2, sub_eval, ei, ret);
 }
 
 HRESULT assign_mul_expression_eval(exec_ctx_t *ctx, expression_t *expr, DWORD flags, jsexcept_t *ei, exprval_t *ret)
diff --git a/dlls/jscript/tests/lang.js b/dlls/jscript/tests/lang.js
index 96df517138..64d3bbdae5 100644
--- a/dlls/jscript/tests/lang.js
+++ b/dlls/jscript/tests/lang.js
@@ -188,6 +188,10 @@ tmp = 1;
 ok((tmp += 1) === 2, "tmp += 1 !== 2");
 ok(tmp === 2, "tmp !== 2");
 
+tmp = 2;
+ok((tmp -= 1) === 1, "tmp -= 1 !== 1");
+ok(tmp === 1, "tmp !=== 1");
+
 tmp = 3 || ok(false, "second or expression called");
 ok(tmp === 3, "3 || (...) is not 3");