diff --git a/include/uuid.h b/include/uuid.h
index 600846f..5f00a49 100644
--- a/include/uuid.h
+++ b/include/uuid.h
@@ -15,7 +15,11 @@
 #include <chrono>
 #include <numeric>
 #include <atomic>
-#include <span>
+#if defined(LIBUUID_CPP20_OR_GREATER)
+# include <span>
+#else
+# include <gsl/span>
+#endif
 
 #ifdef _WIN32
 
@@ -51,7 +55,7 @@
 
 namespace uuids
 {
-#ifdef __cpp_lib_span
+#if defined(LIBUUID_CPP20_OR_GREATER)
    template <class ElementType, std::size_t Extent>
    using span = std::span<ElementType, Extent>;
 #else