diff --git a/lib/node-gd.js b/lib/node-gd.js
index 9b82b5b..ea29dd2 100644
--- a/lib/node-gd.js
+++ b/lib/node-gd.js
@@ -85,9 +85,11 @@ formats.forEach(format => {
     return;
   }
 
-  Object.defineProperty(bindings.Image.prototype, `save${format}`, {
-    value: saveFormatFn(format)
-  });
+  if (!bindings.Image.prototype[`save${format}`]) {
+    Object.defineProperty(bindings.Image.prototype, `save${format}`, {
+      value: saveFormatFn(format)
+    });
+  }
 });
 
 /**