diff --git a/lib/pdf417/number_compactor.ex b/lib/pdf417/number_compactor.ex
index 31bf864..048b3da 100644
--- a/lib/pdf417/number_compactor.ex
+++ b/lib/pdf417/number_compactor.ex
@@ -9,7 +9,7 @@ defmodule PDF417.NumberCompactor do
   end
 
   def compactable?(part) do
-    String.length(part) > 13 && Integer.parse(part) != :error
+    String.length(part) > 13 && String.match?(part, ~r/^\d+$/)
   end
 
   def codeword, do: 902
diff --git a/test/number_compactor_test.exs b/test/number_compactor_test.exs
index 753dce6..958d771 100644
--- a/test/number_compactor_test.exs
+++ b/test/number_compactor_test.exs
@@ -19,10 +19,18 @@ defmodule PDF417.NumberCompactorTest do
       assert NumberCompactor.compactable?("12345678912345")
     end
 
-    test "returns false for strings" do
+    test "returns false for short strings" do
       refute NumberCompactor.compactable?("asdf")
     end
 
+    test "returns false for long strings" do
+      refute NumberCompactor.compactable?("stringgreaterthanthirteencharacters")
+    end
+
+    test "returns false for strings that does not represent a number" do
+      refute NumberCompactor.compactable?("123abcdefghijkl")
+    end
+
     test "returns false for short numbers" do
       refute NumberCompactor.compactable?("123")
     end