diff --git a/Library/Homebrew/env_config.rb b/Library/Homebrew/env_config.rb
index ee7636e5c3..007b80a302 100644
--- a/Library/Homebrew/env_config.rb
+++ b/Library/Homebrew/env_config.rb
@@ -192,7 +192,8 @@ module Homebrew
       HOMEBREW_INSTALL_FROM_API:               {
         description: "If set, install formulae and casks in homebrew/core and homebrew/cask taps using Homebrew's " \
                      "API instead of needing (large, slow) local checkouts of these repositories." \
-                     "\n\n    *Note:* Users with developer mode enabled cannot set HOMEBREW_INSTALL_FROM_API.",
+                     "\n\n    *Note:* Setting HOMEBREW_INSTALL_FROM_API is not compatible with Homebrew's " \
+                     "developer mode so will error (as Homebrew development needs a full clone).",
         boolean:     true,
       },
       HOMEBREW_LIVECHECK_WATCHLIST:            {