5 files changed, 16 insertions, 2 deletions
diff --git a/include/proj/internal/Makefile.am b/include/proj/internal/Makefile.am
index 8e9edacf..b3fb57eb 100644
--- a/include/proj/internal/Makefile.am
+++ b/include/proj/internal/Makefile.am
@@ -1,4 +1,4 @@
-SUBDIRS = nlohmann
+SUBDIRS = vendor
 
 noinst_HEADERS = \
 	coordinatesystem_internal.hpp \
diff --git a/include/proj/internal/include_nlohmann_json.hpp b/include/proj/internal/include_nlohmann_json.hpp
index 68b6836d..6fa5cd2d 100644
--- a/include/proj/internal/include_nlohmann_json.hpp
+++ b/include/proj/internal/include_nlohmann_json.hpp
@@ -26,13 +26,26 @@
  * DEALINGS IN THE SOFTWARE.
  ****************************************************************************/
 
+#ifndef INCLUDE_NLOHMANN_JSON_HPP
+#define INCLUDE_NLOHMANN_JSON_HPP
+
 #if defined(__GNUC__)
 #pragma GCC system_header
 #endif
 
+#ifdef EXTERNAL_NLOHMANN_JSON
+
+#include <nlohmann/json.hpp>
+
+#else // !EXTERNAL_NLOHMANN_JSON
+
 // to avoid any clash if PROJ users have another version of nlohmann/json.hpp
 #define nlohmann proj_nlohmann
 
 #if !defined(DOXYGEN_ENABLED)
-#include "nlohmann/json.hpp"
+#include "vendor/nlohmann/json.hpp"
 #endif
+
+#endif // EXTERNAL_NLOHMANN_JSON
+
+#endif // INCLUDE_NLOHMANN_JSON_HPP
diff --git a/include/proj/internal/vendor/Makefile.am b/include/proj/internal/vendor/Makefile.am
new file mode 100644
index 00000000..7d8176b2
--- /dev/null
+++ b/include/proj/internal/vendor/Makefile.am
@@ -0,0 +1 @@
+SUBDIRS = nlohmann
diff --git a/include/proj/internal/nlohmann/Makefile.am b/include/proj/internal/vendor/nlohmann/Makefile.am
index eaf3200e..eaf3200e 100644
--- a/include/proj/internal/nlohmann/Makefile.am
+++ b/include/proj/internal/vendor/nlohmann/Makefile.am
diff --git a/include/proj/internal/nlohmann/json.hpp b/include/proj/internal/vendor/nlohmann/json.hpp
index a70aaf8c..a70aaf8c 100644
--- a/include/proj/internal/nlohmann/json.hpp
+++ b/include/proj/internal/vendor/nlohmann/json.hpp