diff --git a/man/manual.md b/man/manual.md
index b825e1378..8b52d2800 100644
--- a/man/manual.md
+++ b/man/manual.md
@@ -264,7 +264,7 @@ You can suppress certain types of errors. The format for such a suppression is o
 
 The `error id` is the id that you want to suppress. The easiest way to get it is to use the --template=gcc command line flag. The id is shown in brackets.
 
-The filename may include the wildcard characters \* or ?, which match any sequence of characters or any single character respectively. It is recommended that you use "/" as path separator on all operating systems.
+The filename may include the wildcard characters \* or ?, which match any sequence of characters or any single character respectively. It is recommended that you use "/" as path separator on all operating systems. The filename must match the filename in the reported warning exactly. For instance, if the warning contains a relative path then the suppression must match that relative path.
 
 ## Command line suppression