diff --git a/source-map-support.js b/source-map-support.js
index 6b9bb93..45d824c 100644
--- a/source-map-support.js
+++ b/source-map-support.js
@@ -70,6 +70,7 @@ function retrieveSourceMap(source) {
   if (sourceMappingURL.slice(0, dataUrlPrefix.length).toLowerCase() == dataUrlPrefix) {
     // Support source map URL as a data url
     sourceMapData = new Buffer(sourceMappingURL.slice(dataUrlPrefix.length), "base64").toString();
+    sourceMappingURL = null;
   } else {
     // Support source map URLs relative to the source URL
     sourceMappingURL = supportRelativeURL(source, sourceMappingURL);