diff --git a/src/libutil/tarfile.cc b/src/libutil/tarfile.cc
index 238d0a7a6..5060a8f24 100644
--- a/src/libutil/tarfile.cc
+++ b/src/libutil/tarfile.cc
@@ -17,7 +17,7 @@ static ssize_t callback_read(struct archive * archive, void * _self, const void
     *buffer = self->buffer.data();
 
     try {
-        return self->source->read((char *) self->buffer.data(), 4096);
+        return self->source->read((char *) self->buffer.data(), self->buffer.size());
     } catch (EndOfFile &) {
         return 0;
     } catch (std::exception & err) {
@@ -39,7 +39,7 @@ void TarArchive::check(int err, const std::string & reason)
         throw Error(reason, archive_error_string(this->archive));
 }
 
-TarArchive::TarArchive(Source & source, bool raw) : buffer(4096)
+TarArchive::TarArchive(Source & source, bool raw) : buffer(65536)
 {
     this->archive = archive_read_new();
     this->source = &source;
diff --git a/src/libutil/tarfile.hh b/src/libutil/tarfile.hh
index 24afb710a..237d18c31 100644
--- a/src/libutil/tarfile.hh
+++ b/src/libutil/tarfile.hh
@@ -24,6 +24,7 @@ struct TarArchive {
 
     ~TarArchive();
 };
+
 void unpackTarfile(Source & source, const Path & destDir);
 
 void unpackTarfile(const Path & tarFile, const Path & destDir);