diff --git a/docs/src/man/doctests.md b/docs/src/man/doctests.md
index 75a96d4318..52561b88b2 100644
--- a/docs/src/man/doctests.md
+++ b/docs/src/man/doctests.md
@@ -237,6 +237,10 @@ DocMeta.setdocmeta!(MyPackage, :DocTestSetup, :(using MyPackage); recursive=true
 makedocs(modules=[MyPackage], ...)
 ```
 
+!!! note
+    Make sure to include all (top-level) modules that contain docstrings with doctests in the
+    `modules` argument to [`makedocs`](@ref). Otherwise these doctests will not be run.
+
 ### Block-level setup code
 
 Yet another option is to use the `setup` keyword argument to the `jldoctest` block, which is