diff --git a/g2o/stuff/string_tools.h b/g2o/stuff/string_tools.h
index 7e30e8bb0..6d750e647 100644
--- a/g2o/stuff/string_tools.h
+++ b/g2o/stuff/string_tools.h
@@ -79,7 +79,7 @@ OutputIterator readInts(const char* str, OutputIterator out)
   char* cl  = (char*)str;
   char* cle = cl;
   while (1) {
-    int id = strtol(cl, &cle, 10);
+    long int id = strtol(cl, &cle, 10);
     if (cl == cle)
       break;
     *out++ = id;