diff --git a/fillpdf.module b/fillpdf.module
index da72da10900387f237ebea1f92f467628a40f9a5..5f24a0f11f7c9c7423cb52cc699fba2f6cbd73cf 100644
--- a/fillpdf.module
+++ b/fillpdf.module
@@ -2076,7 +2076,7 @@ function fillpdf_pdftk_check($pdftk_path = 'pdftk') {
     return FALSE;
   }
   // Check if version output includes "pdftk".
-  elseif (!strpos($output, 'pdftk')) {
+  elseif (strpos($output, 'pdftk') === FALSE) {
     return FALSE;
   }
   return TRUE;