diff --git a/lib/output.js b/lib/output.js
index 0dba8d016..c2c2b3a5c 100644
--- a/lib/output.js
+++ b/lib/output.js
@@ -285,8 +285,8 @@ function OutputStream(options) {
     var OUTPUT = new Rope();
     let printed_comments = new Set();
 
-    var to_utf8 = options.ascii_only ? function(str, identifier) {
-        if (options.ecma >= 2015 && !options.safari10) {
+    var to_utf8 = options.ascii_only ? function(str, identifier = false, regexp = false) {
+        if (options.ecma >= 2015 && !options.safari10 && !regexp) {
             str = str.replace(/[\ud800-\udbff][\udc00-\udfff]/g, function(ch) {
                 var code = get_full_char_code(ch, 0).toString(16);
                 return "\\u{" + code + "}";
@@ -2213,7 +2213,7 @@ function OutputStream(options) {
         flags = flags ? sort_regexp_flags(flags) : "";
         source = source.replace(r_slash_script, slash_script_replace);
 
-        output.print(output.to_utf8(`/${source}/${flags}`));
+        output.print(output.to_utf8(`/${source}/${flags}`, false, true));
 
         const parent = output.parent();
         if (
diff --git a/test/compress.js b/test/compress.js
index 8c17c219f..3c18be427 100644
--- a/test/compress.js
+++ b/test/compress.js
@@ -100,7 +100,7 @@ async function run_compress_tests() {
         log_start_file(file);
         async function test_case(test) {
             log_test(test.name);
-            var output_options = test.beautify || {};
+            var output_options = test.beautify || test.format || {};
             var expect;
             if (test.expect) {
                 expect = make_code(as_toplevel(test.expect, test.mangle), output_options);
diff --git a/test/compress/unicode.js b/test/compress/unicode.js
index 36e3e1568..7b6ee1a75 100644
--- a/test/compress/unicode.js
+++ b/test/compress/unicode.js
@@ -189,3 +189,16 @@ issue_3271: {
     }
     expect_stdout: "[ 195, 169 ]"
 }
+
+issue_1147: {
+    format = {
+        ecma: 2015,
+        ascii_only: true,
+        safari10: false
+    }
+    input: {
+        console.log(/📞/.test("📞"))
+    }
+    expect_exact: 'console.log(/\\ud83d\\udcde/.test("\\u{1f4de}"));'
+    expect_stdout: "true"
+}