diff --git a/Library/Homebrew/tab.rb b/Library/Homebrew/tab.rb
index 1cabacefdd..6b274b1438 100644
--- a/Library/Homebrew/tab.rb
+++ b/Library/Homebrew/tab.rb
@@ -317,6 +317,10 @@ class Tab < OpenStruct
   end
 
   def write
+    # If this is a new installation, the cache of installed formulae
+    # will no longer be valid.
+    Formula.clear_cache unless tabfile.exist?
+
     CACHE[tabfile] = self
     tabfile.atomic_write(to_json)
   end
diff --git a/Library/Homebrew/test/keg_test.rb b/Library/Homebrew/test/keg_test.rb
index fdc739c9d8..2c91027e5b 100644
--- a/Library/Homebrew/test/keg_test.rb
+++ b/Library/Homebrew/test/keg_test.rb
@@ -327,7 +327,6 @@ class InstalledDependantsTests < LinkTests
     f = stub_formula_name(name)
     keg = super
     Tab.create(f, DevelopmentTools.default_compiler, :libcxx).write
-    Formula.clear_cache
     keg
   end