diff --git a/builtin/README.md b/builtin/README.md
deleted file mode 100644
index 956ebadf..00000000
--- a/builtin/README.md
+++ /dev/null
@@ -1,9 +0,0 @@
-The Wren scripts in this directory get converted to C string literals into files
-with a `.wren.inc` extension. Those are then `#include`d into their respective
-`.c` files so that the interpreter can load them directly without having to do
-any file IO.
-
-The script that does this translation is `util/wren_to_c_string.py`.
-
-When any of the ".wren" files in here are changed, the Makefile automatically
-updates the generated C headers.
diff --git a/src/README.md b/src/README.md
index c5312ffd..b6c105a9 100644
--- a/src/README.md
+++ b/src/README.md
@@ -1,19 +1,24 @@
 This contains the Wren source code. It is organized like so:
 
-* `cli`: the source code for the command line interface. This is a custom
-  exectuable that embeds the VM in itself. Code here handles reading
-  command-line, running the REPL, loading modules from disc, etc.
+*   `aux`: the Wren and C source code for the auxiliary modules. These are built
+    in to the VM and can be used even when you embed the VM in your own
+    application. But they are also optional and can be compiled out by setting
+    defines.
 
-* `include`: the public header directory for the VM. If you are embedding the
-  VM in your own application, you will add this to your include path.
+*   `cli`: the source code for the command line interface. This is a custom
+    exectuable that embeds the VM in itself. Code here handles reading
+    command-line, running the REPL, loading modules from disc, etc.
 
-* `module`: the source code for the built-in modules that come with the CLI.
-  These modules are written in a mixture of C and Wren and generally use
-  [libuv][] to implement their underlying functionality.
+*   `include`: the public header directory for the VM. If you are embedding the
+    VM in your own application, you will add this to your include path.
 
-* `vm`: the source code for the Wren VM itself. Unlike code in `cli` and
-  `module`, this has no dependencies on libuv. If you are embedding the VM in
-  your own application from source, you will compile the files here into your
-  app.
+*   `module`: the source code for the built-in modules that come with the CLI.
+    These modules are written in a mixture of C and Wren and generally use
+    [libuv][] to implement their underlying functionality.
+
+*   `vm`: the source code for the Wren VM itself. Unlike code in `cli` and
+    `module`, this has no dependencies on libuv. If you are embedding the VM in
+    your own application from source, you will compile the files here into your
+    app.
 
 [libuv]: http://libuv.org/
diff --git a/src/aux/wren_aux_random.wren.inc b/src/aux/wren_aux_random.wren.inc
index 4f39756d..cc2d5b31 100644
--- a/src/aux/wren_aux_random.wren.inc
+++ b/src/aux/wren_aux_random.wren.inc
@@ -1,4 +1,4 @@
-// Generated automatically from src/module/random.wren. Do not edit.
+// Generated automatically from src/aux/wren_aux_random.wren. Do not edit.
 static const char* randomModuleSource =
 "foreign class Random {\n"
 "  construct new() {\n"
diff --git a/builtin/core.wren b/src/vm/wren_core.wren
similarity index 100%
rename from builtin/core.wren
rename to src/vm/wren_core.wren
diff --git a/src/vm/wren_core.wren.inc b/src/vm/wren_core.wren.inc
index 3a81df0e..1fce5623 100644
--- a/src/vm/wren_core.wren.inc
+++ b/src/vm/wren_core.wren.inc
@@ -1,4 +1,4 @@
-// Generated automatically from builtin/core.wren. Do not edit.
+// Generated automatically from src/vm/wren_core.wren. Do not edit.
 static const char* coreModuleSource =
 "class Bool {}\n"
 "class Fiber {}\n"
diff --git a/util/wren.mk b/util/wren.mk
index 21ab9a41..478bdea5 100644
--- a/util/wren.mk
+++ b/util/wren.mk
@@ -208,7 +208,7 @@ $(LIBUV): $(LIBUV_DIR)/build/gyp/gyp util/libuv.py
 src/aux/wren_aux_%.wren.inc: src/aux/wren_aux_%.wren util/wren_to_c_string.py
 	@ ./util/wren_to_c_string.py $@ $<
 
-src/vm/wren_%.wren.inc: builtin/%.wren util/wren_to_c_string.py
+src/vm/wren_%.wren.inc: src/vm/wren_%.wren util/wren_to_c_string.py
 	@ ./util/wren_to_c_string.py $@ $<
 
 src/module/%.wren.inc: src/module/%.wren util/wren_to_c_string.py
diff --git a/util/wren_to_c_string.py b/util/wren_to_c_string.py
index c93b1b1a..f33bc3c6 100755
--- a/util/wren_to_c_string.py
+++ b/util/wren_to_c_string.py
@@ -42,7 +42,8 @@ def main():
     wren_source_lines = f.readlines()
 
   module = os.path.splitext(os.path.basename(args.input))[0]
-  module = module.replace("wren_aux_", "")
+  module = module.replace("aux_", "")
+  module = module.replace("wren_", "")
 
   c_source = wren_to_c_string(args.input, wren_source_lines, module)