diff --git a/.crow/build-all-versions-install-deps.yaml b/.crow/build-all-versions-install-deps.yaml
index 97610df..1c2df64 100644
--- a/.crow/build-all-versions-install-deps.yaml
+++ b/.crow/build-all-versions-install-deps.yaml
@@ -10,10 +10,21 @@ variables:
       - arm64
     default: amd64
   OS:
-    description: "Base OS image name (e.g. alpine, redhat, ubuntu)."
+    description: "Base OS image name."
+    options:
+      - alpine
+      - redhat
+      - ubuntu
     default: alpine
   OS_VERSION:
-    description: "OS version / image tag (e.g. 3.24, 9, jammy, noble)."
+    description: "OS image tag. Must match OS (alpine: 3.24; redhat: 8/9/10; ubuntu: jammy/noble)."
+    options:
+      - "3.24"
+      - "8"
+      - "9"
+      - "10"
+      - "jammy"
+      - "noble"
     default: "3.24"
   R_VERSION:
     description: "Primary R version under /opt/R."
diff --git a/.crow/build-all-versions.yaml b/.crow/build-all-versions.yaml
index b2ede89..517a155 100644
--- a/.crow/build-all-versions.yaml
+++ b/.crow/build-all-versions.yaml
@@ -11,10 +11,21 @@ variables:
       - arm64
     default: amd64
   OS:
-    description: "Base OS image name (e.g. alpine, redhat, ubuntu)."
+    description: "Base OS image name."
+    options:
+      - alpine
+      - redhat
+      - ubuntu
     default: alpine
   OS_VERSION:
-    description: "OS version / image tag (e.g. 3.24, 9, jammy, noble)."
+    description: "OS image tag. Must match OS (alpine: 3.24; redhat: 8/9/10; ubuntu: jammy/noble)."
+    options:
+      - "3.24"
+      - "8"
+      - "9"
+      - "10"
+      - "jammy"
+      - "noble"
     default: "3.24"
   R_VERSION:
     description: "Primary R version under /opt/R."