diff --git a/README.md b/README.md
index 3b9591ab..c276c18c 100644
--- a/README.md
+++ b/README.md
@@ -645,11 +645,15 @@ does not have it.
 ### Sometimes it takes much longer to get semantic completions than normal
 
 This means that libclang (which YCM uses for C-family semantic completion)
-failed to compile your file's preamble. In other words, there was an error
+failed to pre-compile your file's preamble. In other words, there was an error
 compiling some of the source code you pulled in through your header files. I
 suggest calling the `:YcmDiags` command to see what they were (even better, have
 Syntastic installed and call `:lopen`).
 
+Bottom line, if libclang can't pre-compile your file's preamble because there
+were errors in it, you're going to get slow completions because there's no AST
+cache.
+
 ### YCM auto-inserts completion strings I don't want!
 
 This means you probably have some mappings that interfere with YCM's internal