new file mode 100644
--- /dev/null
+++ b/js/src/jit-test/tests/auto-regress/bug1263879.js
@@ -0,0 +1,21 @@
+if (!('oomTest' in this))
+    quit();
+
+var lines = `
+
+
+
+"".replace([[2], 3])
+`.split('\n');
+var code = "";
+while (true) {
+    var line = lines.shift();
+    if (line == null)
+        break;
+    loadFile();
+    code += line + "\n";
+}
+loadFile(code);
+function loadFile(code) {
+    oomTest(() => eval(code));
+}

--- a/js/src/jsstr.cpp
+++ b/js/src/jsstr.cpp
@@ -2304,16 +2304,19 @@ JSString*
 js::str_replace_string_raw(JSContext* cx, HandleString string, HandleString pattern,
                            HandleString replacement)
 {
     RootedLinearString repl(cx, replacement->ensureLinear(cx));
     if (!repl)
         return nullptr;
 
     RootedAtom pat(cx, AtomizeString(cx, pattern));
+    if (!pat)
+        return nullptr;
+
     size_t patternLength = pat->length();
     int32_t match;
     uint32_t dollarIndex;
 
     {
         AutoCheckCannotGC nogc;
         dollarIndex = repl->hasLatin1Chars()
                       ? FindDollarIndex(repl->latin1Chars(nogc), repl->length())