diff --git a/src/aphront/storage/connection/AphrontDatabaseConnection.php b/src/aphront/storage/connection/AphrontDatabaseConnection.php
--- a/src/aphront/storage/connection/AphrontDatabaseConnection.php
+++ b/src/aphront/storage/connection/AphrontDatabaseConnection.php
@@ -8,6 +8,7 @@
   implements PhutilQsprintfInterface {
 
   private $transactionState;
+  private $readOnly;
 
   abstract public function getInsertID();
   abstract public function getAffectedRows();
@@ -37,6 +38,15 @@
     return false;
   }
 
+  public function setReadOnly($read_only) {
+    $this->readOnly = $read_only;
+    return $this;
+  }
+
+  public function getReadOnly() {
+    return $this->readOnly;
+  }
+
   public function asyncQuery($raw_query) {
     throw new Exception(pht('Async queries are not supported.'));
   }
diff --git a/src/aphront/storage/connection/mysql/AphrontBaseMySQLDatabaseConnection.php b/src/aphront/storage/connection/mysql/AphrontBaseMySQLDatabaseConnection.php
--- a/src/aphront/storage/connection/mysql/AphrontBaseMySQLDatabaseConnection.php
+++ b/src/aphront/storage/connection/mysql/AphrontBaseMySQLDatabaseConnection.php
@@ -257,9 +257,17 @@
     //   (SELECT ...) UNION (SELECT ...)
     $is_write = !preg_match('/^[(]*(SELECT|SHOW|EXPLAIN)\s/', $raw_query);
     if ($is_write) {
+      if ($this->getReadOnly()) {
+        throw new Exception(
+          pht(
+            'Attempting to issue a write query on a read-only '.
+            'connection (to database "%s")!',
+            $this->getConfiguration('database')));
+      }
       AphrontWriteGuard::willWrite();
       return true;
     }
+
     return false;
   }