diff --git a/README.md b/README.md
index c0bdee8..306c627 100644
--- a/README.md
+++ b/README.md
@@ -110,6 +110,19 @@ Note that the header included at the bottom must be generated by invoking the co
 reflective_rapidjson_generator --input-file "$srcdir/code-defining-structs.cpp" --output-file "$builddir/reflection/code-defining-structs.h"
 ```
 
+#### Passing further options to Clang
+To pass further options to Clang, just add `--clang-opt` to the arguments, eg. `--clang-opt -DSOME_DEFINE -DANOTHER_DEFINE`.
+It is possible to pass anything from `clang --help`, including the `-X...` options.
+
+---
+
+In case you get a massive number of errors, ensure Clang's resource directory can be located.
+[Clang documentation](https://clang.llvm.org/docs/LibTooling.html#libtooling-builtin-includes):
+
+> The default location to look for builtin headers is in a path `$(dirname /path/to/tool)/../lib/clang/3.3/include` relative to the tool binary.
+
+To adjust the default location, just add eg. `--clang-opt -resource-dir /usr/lib/clang/5.0.1` to the arguments.
+
 #### Invoking code generator with CMake macro
 It is possible to use the provided CMake macro to automate the code generator invocation:
 ```
@@ -140,6 +153,9 @@ will always have the extension "`.h`", independently of the extension of the inp
 The full paths of the generated files are also appended to the variable `LIST_OF_GENERATED_HEADERS` which then can be added
 to the sources of your target. Of course this can be skipped if not required/wanted.
 
+The macro will also automatically pass Clang's resource directory which is detected by invoking `clang -print-resource-dir`.
+To adjust that, just set the cache variable `REFLECTION_GENERATOR_CLANG_RESOURCE_DIR` before including the module.
+
 For an explanation of the `CLANG_OPTIONS_FROM_TARGETS` argument, read the next section.
 
 #### Passing Clang options