diff --git a/src/libfetchers/git.cc b/src/libfetchers/git.cc
index 4a916929e..80c5884f7 100644
--- a/src/libfetchers/git.cc
+++ b/src/libfetchers/git.cc
@@ -38,7 +38,7 @@ const std::string gitInitialBranch = "__nix_dummy_branch";
 
 bool isCacheFileWithinTtl(time_t now, const struct stat & st)
 {
-    return st.st_mtime + settings.tarballTtl > now;
+    return st.st_mtime + static_cast<time_t>(settings.tarballTtl) > now;
 }
 
 Path getCachePath(std::string_view key, bool shallow)