diff --git a/R/build-reference-index.R b/R/build-reference-index.R
index 1f942d7d4..42cd98378 100644
--- a/R/build-reference-index.R
+++ b/R/build-reference-index.R
@@ -173,7 +173,10 @@ check_missing_topics <- function(rows, pkg, error_call = caller_env()) {
       pkg,
       c(
         "{sum(missing)} topic{?s} missing from index: {.val {pkg$topics$name[missing]}}.",
-        i = "Either use {.code @keywords internal} to drop from index, or"
+        i = paste(
+          "Either add to the reference index,",
+          "or use {.code @keywords internal} to drop from the index."
+        )
       ),
       call = error_call
     )
diff --git a/tests/testthat/_snaps/build-reference-index.md b/tests/testthat/_snaps/build-reference-index.md
index 22d449c14..456911031 100644
--- a/tests/testthat/_snaps/build-reference-index.md
+++ b/tests/testthat/_snaps/build-reference-index.md
@@ -57,7 +57,7 @@
     Condition
       Error:
       ! In _pkgdown.yml, 3 topics missing from index: "c", "e", and "?".
-      i Either use `@keywords internal` to drop from index, or
+      i Either add to the reference index, or use `@keywords internal` to drop from the index.
 
 # gives informative errors
 
diff --git a/tests/testthat/_snaps/check.md b/tests/testthat/_snaps/check.md
index 8c8cb3f13..48ad838dc 100644
--- a/tests/testthat/_snaps/check.md
+++ b/tests/testthat/_snaps/check.md
@@ -26,7 +26,7 @@
       v Articles metadata ok.
       x Reference metadata not ok.
         In _pkgdown.yml, 1 topic missing from index: "?".
-        Either use `@keywords internal` to drop from index, or
+        Either add to the reference index, or use `@keywords internal` to drop from the index.
 
 # checks fails on first problem