diff --git a/openvpn/tun/builder/capture.hpp b/openvpn/tun/builder/capture.hpp
index 0b7a0d74..f88d4b97 100644
--- a/openvpn/tun/builder/capture.hpp
+++ b/openvpn/tun/builder/capture.hpp
@@ -150,7 +150,7 @@ class TunBuilderCapture : public TunBuilderBase, public RC<thread_unsafe_refcoun
         std::string to_string() const
         {
             std::ostringstream os;
-            os << address << '/' << prefix_length;
+            os << address << '/' << static_cast<uint16_t>(prefix_length);
             if (!gateway.empty())
                 os << " -> " << gateway;
             if (metric >= 0)
diff --git a/test/unittests/CMakeLists.txt b/test/unittests/CMakeLists.txt
index 70cb8182..2ea39541 100644
--- a/test/unittests/CMakeLists.txt
+++ b/test/unittests/CMakeLists.txt
@@ -67,6 +67,7 @@ add_executable(coreUnitTests
         test_streq.cpp
         test_time.cpp
         test_typeindex.cpp
+        test_tun_builder.cpp
         test_userpass.cpp
         test_validatecreds.cpp
         test_weak.cpp
diff --git a/test/unittests/test_tun_builder.cpp b/test/unittests/test_tun_builder.cpp
new file mode 100644
index 00000000..4ec6d7a6
--- /dev/null
+++ b/test/unittests/test_tun_builder.cpp
@@ -0,0 +1,14 @@
+
+#include "test_common.h"
+
+#include <openvpn/tun/builder/capture.hpp>
+
+TEST(tun_builder, to_string_zero)
+{
+    auto rb = openvpn::TunBuilderCapture::RouteBase();
+
+    rb.address = "0.0.0.0";
+    rb.prefix_length = 0;
+
+    EXPECT_EQ(rb.to_string(), "0.0.0.0/0");
+}
\ No newline at end of file