diff --git a/lib/source-map-consumer.js b/lib/source-map-consumer.js
index aa3357d7..b2db4d55 100644
--- a/lib/source-map-consumer.js
+++ b/lib/source-map-consumer.js
@@ -301,7 +301,9 @@ class BasicSourceMapConsumer extends SourceMapConsumer {
     const aStr = this._mappings;
     const size = aStr.length;
 
-    const mappingsBufPtr = this._wasm.exports.allocate_mappings(size);
+    // Interpret signed result of allocate_mappings as unsigned, otherwise
+    // addresses higher than 2GB will be negative.
+    const mappingsBufPtr = this._wasm.exports.allocate_mappings(size) >>> 0;
     const mappingsBuf = new Uint8Array(
       this._wasm.exports.memory.buffer,
       mappingsBufPtr,