diff --git a/doc/guides/contributing/pull-requests.md b/doc/guides/contributing/pull-requests.md
index 352c6eba39e04e..228b9839ca1f8b 100644
--- a/doc/guides/contributing/pull-requests.md
+++ b/doc/guides/contributing/pull-requests.md
@@ -251,7 +251,9 @@ And on Windows:
 > vcbuild test
 ```
 
-(See the [running tests][] section of Building guide for more details.)
+For some configurations, running all tests might take a long time (an hour or
+more). To run a subset of the test suite, see the [running tests][] section of
+the Building guide.
 
 ### Step 7: Push