--- a/js/src/configure.in
+++ b/js/src/configure.in
@@ -144,16 +144,17 @@ else
   JS_SHARED_LIBRARY=1
 fi
 AC_SUBST(JS_SHARED_LIBRARY)
 
 if test "$JS_STANDALONE" = no; then
   JS_STANDALONE=
 else
   JS_STANDALONE=1
+  AC_DEFINE(JS_STANDALONE)
 fi
 AC_SUBST(JS_STANDALONE)
 
 MOZ_ARG_WITH_STRING(gonk,
 [  --with-gonk=DIR
                location of gonk dir],
     gonkdir=$withval)
 

--- a/js/src/jit/AsmJSSignalHandlers.cpp
+++ b/js/src/jit/AsmJSSignalHandlers.cpp
@@ -1028,8 +1028,20 @@ js::TriggerOperationCallbackForAsmJSCode
     DWORD oldProtect;
     if (!VirtualProtect(module.functionCode(), module.functionBytes(), PAGE_NOACCESS, &oldProtect))
         MOZ_CRASH();
 #else  // assume Unix
     if (mprotect(module.functionCode(), module.functionBytes(), PROT_NONE))
         MOZ_CRASH();
 #endif
 }
+
+#ifdef MOZ_ASAN
+#ifdef JS_STANDALONE
+// Usually, this definition is found in mozglue (see mozglue/build/AsanOptions.cpp).
+// However, when doing standalone JS builds, mozglue is not used and we must ensure
+// that we still allow custom SIGSEGV handlers for asm.js and ion to work correctly.
+extern "C" MOZ_ASAN_BLACKLIST
+const char* __asan_default_options() {
+    return "allow_user_segv_handler=1";
+}
+#endif
+#endif