diff --git a/api/external_api.php b/api/external_api.php
index c59a50e..748d0c3 100644
--- a/api/external_api.php
+++ b/api/external_api.php
@@ -75,13 +75,8 @@ class external_api extends cora\api {
       curl_setopt($curl_handle, CURLINFO_HEADER_OUT, true);
     }
 
-    $should_cache = (
-      $this::$cache === true &&
-      $this::should_cache($arguments) === true
-    );
-
     // Check the cache
-    if ($should_cache === true) {
+    if ($this::$cache === true) {
       $cache_key = $this->generate_cache_key($arguments);
       $cache_entry = $this->get_cache_entry($cache_key);
     } else {
@@ -116,7 +111,10 @@ class external_api extends cora\api {
         $this->log_mysql($curl_response);
       }
 
-      if($should_cache === true) {
+      if(
+        $this::$cache === true &&
+        $this::should_cache($arguments, $curl_response, $this->curl_info) === true
+      ) {
         $this->create_update_cache_entry($cache_key, $curl_response);
       }
 
diff --git a/api/smarty_streets.php b/api/smarty_streets.php
index 09115b9..8b21a21 100644
--- a/api/smarty_streets.php
+++ b/api/smarty_streets.php
@@ -58,11 +58,8 @@ class smarty_streets extends external_api {
     ]);
 
     $response = json_decode($curl_response, true);
-    if ($response === null) {
-      throw new Exception('Invalid JSON');
-    }
 
-    if (count($response) === 0) {
+    if ($response === null || count($response) === 0) {
       return null;
     } else {
       // Smarty doesn't return this but I want it.
@@ -85,14 +82,19 @@ class smarty_streets extends external_api {
   }
 
   /**
-   * Determine whether or not a request should be cached. For this, just cache
-   * everything.
+   * Determine whether or not a request should be cached. For this, cache
+   * valid JSON responses with status code 200.
    *
    * @param array $arguments
+   * @param string $curl_response
+   * @param array $curl_info
    *
    * @return boolean
    */
-  protected function should_cache($arguments) {
-    return true;
+  protected function should_cache($arguments, $curl_response, $curl_info) {
+    return (
+      $curl_info['http_code'] === 200 &&
+      json_decode($curl_response, true) !== null
+    );
   }
 }