diff --git a/core/product_config.rbc b/core/product_config.rbc
index ef0d0c9..8fbcfa5 100644
--- a/core/product_config.rbc
+++ b/core/product_config.rbc
@@ -439,7 +439,7 @@
     """Returns regular expression equivalent to Make pattern."""
 
     # TODO(asmundak): this will mishandle '\%'
-    return "^(" + "|".join([w.replace("%", ".*", 1) for w in words]) + ")"
+    return "^(" + "|".join([w.replace("%", ".*", 1) for w in words if w]) + ")$"
 
 def _regex_match(regex, w):
     return rblf_regex(regex, w)
diff --git a/tests/run.rbc b/tests/run.rbc
index 4d7166a..2c15b81 100644
--- a/tests/run.rbc
+++ b/tests/run.rbc
@@ -47,6 +47,9 @@
 assert_eq(["foo/%"], rblf.mkpatsubst("%", "%/%", ["foo"]))
 assert_eq(["from/a:to/a", "from/b:to/b"], rblf.product_copy_files_by_pattern("from/%", "to/%", "a b"))
 
+assert_eq([], rblf.filter(["a", "", "b"], "f"))
+assert_eq(["", "b"], rblf.filter_out(["a", "" ], ["a", "", "b"] ))
+
 globals, config = rblf.product_configuration("test/device", init)
 assert_eq(
     {