diff --git a/Project-Setup.md b/Project-Setup.md
index 2756380..098fc32 100644
--- a/Project-Setup.md
+++ b/Project-Setup.md
@@ -134,9 +134,11 @@ with open(os.path.join(sys.argv[1], 'compile_commands.json')) as f:
 
 ## `.ccls` File
 
-`.ccls` is a line-based text file at the project root.  Its main function is
-to specify compiler flags needed to properly index your code: `-I` `-D` etc.
-Each line consists of one argument to be added to the compiler command line.
+`.ccls` is a line-based text file at the project root. Its specifies compiler
+flags needed to properly index your code: `-I` `-D` etc.  The first line
+specifies the compiler driver (usually `clang`), while each subsequent lines
+specifies one argument to be added to the compiler command line.
+
 No whitespace splitting is performed on the argument, thus `-I foo` cannot be
 used (use `-Ifoo` or `-I\nfoo` for example).
 
@@ -151,9 +153,10 @@ Available directives include:
 ### `%compile_commands.json`
 
 By default `.ccls` compiler flags are applied _only_ to files not listed in
-`compile_commands.json`.  If this directive appears first in `.ccls` then after
-`compile_commands.json` is parsed, the rest of the `.ccls` arguments will be
-_appended_ to the compiler flags for files found in `compile_commands.json`.
+`compile_commands.json`.  If this directive appears first in `.ccls`, the
+compiler driver must be omitted. After `compile_commands.json` is parsed, the
+rest of the `.ccls` arguments will be _appended_ to the compiler flags for
+files found in `compile_commands.json`.
 
 ### `%c` / `%cpp` / `%objective-c` / `%objective-cpp`
 
@@ -182,7 +185,7 @@ You may run into parsing errors like `unknown type name 'class'`.
 
 ### Compiler driver
 
-Just use `clang` as the compiler driver (the first line unless `%compile_commands.json` is used).
+Unless `%compile_commands.json` is used, you _must_ specify a "compiler driver" as the first line of your `.ccls` file.
 
 * `clang` defaults to GCCMode (gcc). It correctly treats `.c` files as C and `.cpp` files as C++.
 * `clang++` defaults to GXXMode (g++). It treats a `.c` file as C++ and issues a warning.