diff --git a/.github/workflows/rebuild-country.yml b/.github/workflows/rebuild-country.yml
index dd6c4a60f..59bbce43c 100644
--- a/.github/workflows/rebuild-country.yml
+++ b/.github/workflows/rebuild-country.yml
@@ -14,7 +14,7 @@ on:
         description: "Short name for this trial build, for prefixing the uploaded data and results files. WARNING: without this we will overwrite files in s3://nextstrain-ncov-private and the trees on nextstrain.org/ncov/gisaid..."
         required: false
       image:
-        description: 'Specific container image to use for build (will override the default of "nextstrain build")'
+        description: 'Specific container image to use for build (e.g. `nextstrain/base:branch-test`, `ghcr.io/user/repo:tag`)'
         required: false
 
 env:
diff --git a/.github/workflows/rebuild-gisaid-21L.yml b/.github/workflows/rebuild-gisaid-21L.yml
index e80191377..561b984f5 100644
--- a/.github/workflows/rebuild-gisaid-21L.yml
+++ b/.github/workflows/rebuild-gisaid-21L.yml
@@ -14,7 +14,7 @@ on:
         description: "Short name for this trial build, for prefixing the uploaded data and results files. WARNING: without this we will overwrite files in s3://nextstrain-ncov-private and the trees on nextstrain.org/ncov/gisaid..."
         required: false
       image:
-        description: 'Specific container image to use for build (will override the default of "nextstrain build")'
+        description: 'Specific container image to use for build (e.g. `nextstrain/base:branch-test`, `ghcr.io/user/repo:tag`)'
         required: false
 
 env:
diff --git a/.github/workflows/rebuild-gisaid.yml b/.github/workflows/rebuild-gisaid.yml
index 1c8cb01fd..820062296 100644
--- a/.github/workflows/rebuild-gisaid.yml
+++ b/.github/workflows/rebuild-gisaid.yml
@@ -14,7 +14,7 @@ on:
         description: "Short name for this trial build, for prefixing the uploaded data and results files. WARNING: without this we will overwrite files in s3://nextstrain-ncov-private and the trees on nextstrain.org/ncov/gisaid..."
         required: false
       image:
-        description: 'Specific container image to use for build (will override the default of "nextstrain build")'
+        description: 'Specific container image to use for build (e.g. `nextstrain/base:branch-test`, `ghcr.io/user/repo:tag`)'
         required: false
 
 env:
diff --git a/.github/workflows/rebuild-open.yml b/.github/workflows/rebuild-open.yml
index fa808c9fd..6b38e05d9 100644
--- a/.github/workflows/rebuild-open.yml
+++ b/.github/workflows/rebuild-open.yml
@@ -15,7 +15,7 @@ on:
         description: "Short name for this trial build, for prefixing the uploaded data and results files. WARNING: without this we will overwrite files in s3://nextstrain-data/files/ncov/open/ and the trees on nextstrain.org/ncov/open/..."
         required: false
       image:
-        description: 'Specific container image to use for build (will override the default of "nextstrain build")'
+        description: 'Specific container image to use for build (e.g. `nextstrain/base:branch-test`, `ghcr.io/user/repo:tag`)'
         required: false
 
 env: