diff --git a/js/src/jit-test/tests/parser/bug-1470992.js b/js/src/jit-test/tests/parser/bug-1470992.js
new file mode 100644
index 000000000000..e03828418ed7
--- /dev/null
+++ b/js/src/jit-test/tests/parser/bug-1470992.js
@@ -0,0 +1,5 @@
+if (helperThreadCount() === 0)
+    quit();
+
+offThreadCompileModule("export { x };");
+gcslice(10);
diff --git a/js/src/jsapi.cpp b/js/src/jsapi.cpp
index a478caf2bcbe..66a76ec626e0 100644
--- a/js/src/jsapi.cpp
+++ b/js/src/jsapi.cpp
@@ -6102,34 +6102,13 @@ JS_DecodeBytes(JSContext* cx, const char* src, size_t srclen, char16_t* dst, siz
     return true;
 }
 
-static char*
-EncodeLatin1(JSContext* cx, JSString* str)
-{
-    JSLinearString* linear = str->ensureLinear(cx);
-    if (!linear)
-        return nullptr;
-
-    JS::AutoCheckCannotGC nogc;
-    if (linear->hasTwoByteChars())
-        return JS::LossyTwoByteCharsToNewLatin1CharsZ(cx, linear->twoByteRange(nogc)).c_str();
-
-    size_t len = str->length();
-    Latin1Char* buf = cx->pod_malloc<Latin1Char>(len + 1);
-    if (!buf)
-        return nullptr;
-
-    mozilla::PodCopy(buf, linear->latin1Chars(nogc), len);
-    buf[len] = '\0';
-    return reinterpret_cast<char*>(buf);
-}
-
 JS_PUBLIC_API(char*)
 JS_EncodeString(JSContext* cx, JSString* str)
 {
     AssertHeapIsIdle();
     CHECK_REQUEST(cx);
 
-    return EncodeLatin1(cx, str);
+    return js::EncodeLatin1(cx, str).release();
 }
 
 JS_PUBLIC_API(char*)
diff --git a/js/src/vm/JSAtom.cpp b/js/src/vm/JSAtom.cpp
index 0677621a9817..648c07ea8141 100644
--- a/js/src/vm/JSAtom.cpp
+++ b/js/src/vm/JSAtom.cpp
@@ -121,7 +121,8 @@ js::AtomToPrintableString(JSContext* cx, JSAtom* atom, JSAutoByteString* bytes)
     JSString* str = QuoteString(cx, atom, 0);
     if (!str)
         return nullptr;
-    return bytes->encodeLatin1(cx, str);
+    bytes->initBytes(EncodeLatin1(cx, str));
+    return bytes->ptr();
 }
 
 #define DEFINE_PROTO_STRING(name,init,clasp) const char js_##name##_str[] = #name;
diff --git a/js/src/vm/StringType.cpp b/js/src/vm/StringType.cpp
index 8b8d49d4f7d4..12a4b3db33f0 100644
--- a/js/src/vm/StringType.cpp
+++ b/js/src/vm/StringType.cpp
@@ -2007,6 +2007,29 @@ JSString::fillWithRepresentatives(JSContext* cx, HandleArrayObject array)
 
 /*** Conversions *********************************************************************************/
 
+UniqueChars
+js::EncodeLatin1(JSContext* cx, JSString* str)
+{
+    JSLinearString* linear = str->ensureLinear(cx);
+    if (!linear)
+        return nullptr;
+
+    JS::AutoCheckCannotGC nogc;
+    if (linear->hasTwoByteChars()) {
+        Latin1CharsZ chars = JS::LossyTwoByteCharsToNewLatin1CharsZ(cx, linear->twoByteRange(nogc));
+        return UniqueChars(chars.c_str());
+    }
+
+    size_t len = str->length();
+    Latin1Char* buf = cx->pod_malloc<Latin1Char>(len + 1);
+    if (!buf)
+        return nullptr;
+
+    mozilla::PodCopy(buf, linear->latin1Chars(nogc), len);
+    buf[len] = '\0';
+    return UniqueChars(reinterpret_cast<char*>(buf));
+}
+
 const char*
 js::ValueToPrintableLatin1(JSContext* cx, const Value& vArg, JSAutoByteString* bytes,
                            bool asSource)
diff --git a/js/src/vm/StringType.h b/js/src/vm/StringType.h
index 3e39e4224dc6..8638fe7ff8b3 100644
--- a/js/src/vm/StringType.h
+++ b/js/src/vm/StringType.h
@@ -1589,6 +1589,12 @@ SubstringKernel(JSContext* cx, HandleString str, int32_t beginInt, int32_t lengt
 
 /*** Conversions *********************************************************************************/
 
+/*
+ * Convert a string to a printable C string.
+ */
+UniqueChars
+EncodeLatin1(JSContext* cx, JSString* str);
+
 /*
  * Convert a value to a printable C string.
  *