diff --git a/src/tools/hardlink_packages.py b/src/tools/hardlink_packages.py
index 125287b389..701b618b95 100755
--- a/src/tools/hardlink_packages.py
+++ b/src/tools/hardlink_packages.py
@@ -46,7 +46,7 @@ for filename in os.listdir(args_src):
 pattern = re.compile("^[a-z0-9]")
 newFileForJam = []
 packageFiles = []
-filesNotFound = False
+errorsOccurred = False
 with open(args_jamf) as f:
 	for line in f:
 		pkg = line.strip()
@@ -75,14 +75,16 @@ with open(args_jamf) as f:
 		if (greatestVersion == None):
 			print("not found: " + pkg)
 			newFileForJam.append(line)
-			filesNotFound = True
+			errorsOccurred = True
 			continue
 		else:
 			# found it, so hardlink it
 			if not (os.path.exists(args_dst_packages + greatestVersion)):
 				os.link(args_src + greatestVersion, args_dst_packages + greatestVersion)
-			if ('packages/' + greatestVersion) not in packageFiles:
-				packageFiles.append('packages/' + greatestVersion)
+			if ('packages/' + greatestVersion) in packageFiles:
+				print("error: duplicated package: " + pkgname)
+				errorsOccurred = True
+			packageFiles.append('packages/' + greatestVersion)
 			# also hardlink the source package, if one exists
 			srcpkg = greatestVersion.replace("-" + args_arch + ".hpkg",
 				"-source.hpkg").replace('-', '_source-', 1)
@@ -93,7 +95,7 @@ with open(args_jamf) as f:
 					packageFiles.append('packages/' + srcpkg)
 		newFileForJam.append("\t" + greatestVersion[:greatestVersion.rfind('-')] + "\n");
 
-if filesNotFound:
+if errorsOccurred:
 	sys.exit(1)
 
 finalizedNewFile = "".join(newFileForJam).encode('UTF-8')