diff --git a/lib/sourcemap.js b/lib/sourcemap.js
index 3ca9f9a8..232cfabd 100644
--- a/lib/sourcemap.js
+++ b/lib/sourcemap.js
@@ -133,7 +133,7 @@ function SourceMap(options) {
                     if (orig_col >= col) indices = segments[i];
                     if (orig_col <= col) break;
                 }
-                if (!indices) return;
+                if (!indices || indices.length < 4) return;
                 source = map.sources[indices[1]];
                 orig_line = indices[2];
                 orig_col = indices[3];