diff --git a/src/libutil/references.cc b/src/libutil/references.cc
index 74003584a..7f59b4c09 100644
--- a/src/libutil/references.cc
+++ b/src/libutil/references.cc
@@ -75,7 +75,7 @@ RewritingSink::RewritingSink(const std::string & from, const std::string & to, S
 RewritingSink::RewritingSink(const StringMap & rewrites, Sink & nextSink)
     : rewrites(rewrites), nextSink(nextSink)
 {
-    long unsigned int maxRewriteSize = 0;
+    std::string::size_type maxRewriteSize = 0;
     for (auto & [from, to] : rewrites) {
         assert(from.size() == to.size());
         maxRewriteSize = std::max(maxRewriteSize, from.size());
diff --git a/src/libutil/references.hh b/src/libutil/references.hh
index ffd730e7b..f0baeffe1 100644
--- a/src/libutil/references.hh
+++ b/src/libutil/references.hh
@@ -26,7 +26,7 @@ public:
 struct RewritingSink : Sink
 {
     const StringMap rewrites;
-    long unsigned int maxRewriteSize;
+    std::string::size_type maxRewriteSize;
     std::string prev;
     Sink & nextSink;
     uint64_t pos = 0;