diff --git a/dmd/json.d b/dmd/json.d
index 913ca2f170..e1efe6c73f 100644
--- a/dmd/json.d
+++ b/dmd/json.d
@@ -955,7 +955,8 @@ Params:
 Returns: JsonFieldFlags.none on error, otherwise the JsonFieldFlags value
          corresponding to the given fieldName.
 */
-JsonFieldFlags tryParseJsonField(const(char)* fieldName)
+// IN_LLVM: was `JsonField tryParseJsonField(const(char)* fieldName)`
+extern (C++) uint tryParseJsonField(const(char)* fieldName)
 {
     auto fieldNameString = fieldName[0 .. strlen(fieldName)];
     foreach (idx, enumName; __traits(allMembers, JsonFieldFlags))
diff --git a/dmd/json.h b/dmd/json.h
index f52dfd4d57..f345628ae2 100644
--- a/dmd/json.h
+++ b/dmd/json.h
@@ -21,5 +21,9 @@ struct OutBuffer;
 
 void json_generate(OutBuffer *, Modules *);
 
+#ifdef IN_LLVM
+unsigned tryParseJsonField(const char *fieldName);
+#endif
+
 #endif /* DMD_JSON_H */
 
diff --git a/driver/cl_options.cpp b/driver/cl_options.cpp
index 6a05e86bb7..8082b45b46 100644
--- a/driver/cl_options.cpp
+++ b/driver/cl_options.cpp
@@ -195,6 +195,9 @@ cl::opt<std::string> jsonFile("Xf", cl::desc("Write JSON file to <filename>"),
                               cl::value_desc("filename"), cl::Prefix,
                               cl::ZeroOrMore);
 
+// supported by DMD, but still undocumented
+cl::list<std::string> jsonFields("Xi", cl::ReallyHidden, cl::value_desc("field"));
+
 // Header generation options
 static cl::opt<bool, true>
     doHdrGen("H", cl::desc("Generate 'header' file"), cl::ZeroOrMore,
diff --git a/driver/cl_options.h b/driver/cl_options.h
index 0471ad4f6e..f4d0583fb1 100644
--- a/driver/cl_options.h
+++ b/driver/cl_options.h
@@ -59,6 +59,7 @@ extern cl::opt<cl::boolOrDefault> output_o;
 extern cl::opt<std::string> ddocDir;
 extern cl::opt<std::string> ddocFile;
 extern cl::opt<std::string> jsonFile;
+extern cl::list<std::string> jsonFields;
 extern cl::opt<std::string> hdrDir;
 extern cl::opt<std::string> hdrFile;
 extern cl::opt<bool> hdrKeepAllBodies;
diff --git a/driver/main.cpp b/driver/main.cpp
index 9d032cb407..76ce9ef527 100644
--- a/driver/main.cpp
+++ b/driver/main.cpp
@@ -423,6 +423,15 @@ void parseCommandLine(int argc, char **argv, Strings &sourceFiles,
   toWinPaths(global.params.fileImppath);
 #endif
 
+  for (const auto &field : jsonFields) {
+    const unsigned flag = tryParseJsonField(field.c_str());
+    if (flag == 0) {
+      error(Loc(), "unknown JSON field `-Xi=%s`", field.c_str());
+    } else {
+      global.params.jsonFieldFlags |= flag;
+    }
+  }
+
   includeImports = !opts::includeModulePatterns.empty();
   for (const auto &pattern : opts::includeModulePatterns) {
     // a value-less `-i` only enables `includeImports`