diff --git a/lib/docsplit/pdf_extractor.rb b/lib/docsplit/pdf_extractor.rb
index 12069c7..5829ecb 100644
--- a/lib/docsplit/pdf_extractor.rb
+++ b/lib/docsplit/pdf_extractor.rb
@@ -23,7 +23,7 @@ def version_string
       unless @@version_string
         null = windows? ? "NUL" : "/dev/null"
         @@version_string = `#{office_executable} -h 2>#{null}`.split("\n").first
-        if !!@@version_string.match(/[0-9]*/)
+        if !!@@version_string.to_s.match(/[0-9]*/)
           @@version_string = `#{office_executable} --version`.split("\n").first
         end
       end