diff --git a/Library/Homebrew/formula_support.rb b/Library/Homebrew/formula_support.rb
index 1ef4d3abc3..69420ff0f8 100644
--- a/Library/Homebrew/formula_support.rb
+++ b/Library/Homebrew/formula_support.rb
@@ -40,6 +40,8 @@ class SoftwareSpec
     when nil    then Version.detect(url, specs)
     when String then Version.new(val)
     when Hash   then Version.new_with_scheme(*val.shift)
+    else
+      raise TypeError, "version '#{val.inspect}' should be a string"
     end
   end
 
diff --git a/Library/Homebrew/test/test_software_spec.rb b/Library/Homebrew/test/test_software_spec.rb
index f3eed4769e..856bea611d 100644
--- a/Library/Homebrew/test/test_software_spec.rb
+++ b/Library/Homebrew/test/test_software_spec.rb
@@ -66,6 +66,12 @@ class SoftwareSpecTests < Test::Unit::TestCase
     assert @spec.version.detected_from_url?
   end
 
+  def test_rejects_non_string_versions
+    assert_raises(TypeError) { @spec.version(1) }
+    assert_raises(TypeError) { @spec.version(2.0) }
+    assert_raises(TypeError) { @spec.version(Object.new) }
+  end
+
   def test_mirrors
     assert_empty @spec.mirrors
     @spec.mirror('foo')