diff --git a/js/ref/jsatom.c b/js/ref/jsatom.c
index 410ac6871f8..86ce81db73c 100644
--- a/js/ref/jsatom.c
+++ b/js/ref/jsatom.c
@@ -111,8 +111,18 @@ js_compare_atom_keys(const void *k1, const void *k2)
     v1 = (jsval)k1, v2 = (jsval)k2;
     if (JSVAL_IS_STRING(v1) && JSVAL_IS_STRING(v2))
 	return !js_CompareStrings(JSVAL_TO_STRING(v1), JSVAL_TO_STRING(v2));
-    if (JSVAL_IS_DOUBLE(v1) && JSVAL_IS_DOUBLE(v2))
-	return *JSVAL_TO_DOUBLE(v1) == *JSVAL_TO_DOUBLE(v2);
+    if (JSVAL_IS_DOUBLE(v1) && JSVAL_IS_DOUBLE(v2)) {
+        double d1 = *JSVAL_TO_DOUBLE(v1);
+        double d2 = *JSVAL_TO_DOUBLE(v2);
+#ifdef XP_PC
+	/* XXX MSVC miscompiles such that (NaN == 0) */
+	if (JSDOUBLE_IS_NaN(d1))
+	    return JSDOUBLE_IS_NaN(d2);
+	else if (JSDOUBLE_IS_NaN(d2))
+            return JS_FALSE;
+#endif
+	return d1 == d2;
+    }
     return v1 == v2;
 }