diff --git a/Library/Homebrew/build.rb b/Library/Homebrew/build.rb
index 1ba4a72793..7d53074cde 100644
--- a/Library/Homebrew/build.rb
+++ b/Library/Homebrew/build.rb
@@ -57,7 +57,7 @@ class Build
       build = effective_build_options_for(dependent)
       if dep.prune_from_option?(build) ||
          dep.prune_if_build_and_not_dependent?(dependent, formula) ||
-         (dep.test? && !dep.build?)
+         (dep.test? && !dep.build?) || dep.implicit?
         Dependency.prune
       elsif dep.build?
         Dependency.keep_but_prune_recursive_deps