diff --git a/src/main/java/com/google/devtools/build/lib/analysis/starlark/StarlarkSubrule.java b/src/main/java/com/google/devtools/build/lib/analysis/starlark/StarlarkSubrule.java
index 5329cb4..bdaf58c 100644
--- a/src/main/java/com/google/devtools/build/lib/analysis/starlark/StarlarkSubrule.java
+++ b/src/main/java/com/google/devtools/build/lib/analysis/starlark/StarlarkSubrule.java
@@ -382,7 +382,9 @@
             /* resolveToolchainDataFunc= */ ruleContext::getToolchainInfo,
             /* resolvedToolchainTypeLabels= */ getAutomaticExecGroupLabels());
       } else {
-        throw Starlark.errorf("subrules using toolchains must enable automatic exec-groups");
+        throw Starlark.errorf(
+            "subrules using toolchains must enable automatic exec-groups. For more info, see"
+                + " https://bazel.build/extending/auto-exec-groups#migration-aegs");
       }
     }
 
diff --git a/src/main/java/com/google/devtools/build/lib/starlarkbuildapi/StarlarkRuleFunctionsApi.java b/src/main/java/com/google/devtools/build/lib/starlarkbuildapi/StarlarkRuleFunctionsApi.java
index eb9f739..d2824b8 100644
--- a/src/main/java/com/google/devtools/build/lib/starlarkbuildapi/StarlarkRuleFunctionsApi.java
+++ b/src/main/java/com/google/devtools/build/lib/starlarkbuildapi/StarlarkRuleFunctionsApi.java
@@ -988,7 +988,10 @@
                 "If set, the set of toolchains this subrule requires. The list can contain String,"
                     + " Label, or StarlarkToolchainTypeApi objects, in any combination. Toolchains"
                     + " will be found by checking the current platform, and provided to the subrule"
-                    + " implementation via <code>ctx.toolchains</code>."),
+                    + " implementation via <code>ctx.toolchains</code>. Note that AEGs need to be"
+                    + " enabled on the consuming rule(s) if this parameter is set. In case you"
+                    + " haven't migrated to AEGs yet, see"
+                    + " https://bazel.build/extending/auto-exec-groups#migration-aegs."),
         @Param(
             name = "fragments",
             allowedTypes = {@ParamType(type = Sequence.class, generic1 = String.class)},