diff --git a/ext/json.cmake b/ext/json.cmake
index 9824519..35fa61f 100644
--- a/ext/json.cmake
+++ b/ext/json.cmake
@@ -1,15 +1,20 @@
-include(FetchContent)
+if(USE_EXTERNAL_JSON)
+  add_library(nlohmann_json INTERFACE IMPORTED)
+  Set_property(TARGET nlohmann_json PROPERTY INTERFACE_INCLUDE_DIRECTORIES "${JSON_SOURCES}/include")
+else()
+  include(FetchContent)
+  
+  FetchContent_Declare(
+          nlohmann_json_ext
+          URL "https://github.com/nlohmann/json/releases/download/v3.7.3/include.zip"
+  )
+  
+  FetchContent_GetProperties(nlohmann_json_ext)
+  if(NOT nlohmann_json_ext_POPULATED)
+    FetchContent_Populate(nlohmann_json_ext)
+  endif()
 
-FetchContent_Declare(
-        nlohmann_json_ext
-        URL "https://github.com/nlohmann/json/releases/download/v3.7.3/include.zip"
-)
-
-FetchContent_GetProperties(nlohmann_json_ext)
-if(NOT nlohmann_json_ext_POPULATED)
-  FetchContent_Populate(nlohmann_json_ext)
+  Add_library(nlohmann_json INTERFACE IMPORTED)
+  Add_dependencies(nlohmann_json nlohmann_json_ext)
+  Set_property(TARGET nlohmann_json PROPERTY INTERFACE_INCLUDE_DIRECTORIES "${nlohmann_json_ext_SOURCE_DIR}/include")
 endif()
-
-add_library(nlohmann_json INTERFACE IMPORTED)
-add_dependencies(nlohmann_json nlohmann_json_ext)
-set_property(TARGET nlohmann_json PROPERTY INTERFACE_INCLUDE_DIRECTORIES "${nlohmann_json_ext_SOURCE_DIR}/include")
\ No newline at end of file