diff --git a/tools/merge_requirements.py b/tools/merge_requirements.py
index 521d28b8f..0d41d12c4 100755
--- a/tools/merge_requirements.py
+++ b/tools/merge_requirements.py
@@ -55,21 +55,24 @@ def main(*paths):
     """Merges multiple requirements files together and prints the result.
 
     Requirement files specified later in the list take precedence over earlier
-    files.
+    files. Files are read from file paths passed from the command line arguments.
 
-    :param tuple paths: paths to requirements files
+    If no command line arguments are defined, data is read from stdin instead.
+
+    :param tuple paths: paths to requirements files provided on command line
 
     """
     data = {}
-    for path in paths:
-        data.update(process_entries(read_file(path)))
-
-    # Need to check if interactive to avoid blocking if nothing is piped
-    if not sys.stdin.isatty():
-        stdin_data = []
-        for line in sys.stdin:
-            stdin_data.append(line)
-        data.update(process_entries(stdin_data))
+    if paths:
+        for path in paths:
+            data.update(process_entries(read_file(path)))
+    else:
+        # Need to check if interactive to avoid blocking if nothing is piped
+        if not sys.stdin.isatty():
+            stdin_data = []
+            for line in sys.stdin:
+                stdin_data.append(line)
+            data.update(process_entries(stdin_data))
 
     return output_requirements(data)
 
diff --git a/tools/pip_install.py b/tools/pip_install.py
index 8f0437d9c..15dc2f0c0 100755
--- a/tools/pip_install.py
+++ b/tools/pip_install.py
@@ -48,7 +48,7 @@ def certbot_normal_processing(tools_path, test_constraints):
     with open(certbot_requirements, 'r') as fd:
         data = fd.readlines()
     with open(test_constraints, 'w') as fd:
-        data = os.linesep.join(strip_hashes.process_entries(data))
+        data = "\n".join(strip_hashes.process_entries(data))
         fd.write(data)
 
 
diff --git a/tools/strip_hashes.py b/tools/strip_hashes.py
index 7e7809458..988e72eb8 100755
--- a/tools/strip_hashes.py
+++ b/tools/strip_hashes.py
@@ -2,7 +2,6 @@
 """Removes hash information from requirement files passed to it as file path
 arguments or simply piped to stdin."""
 
-import os
 import re
 import sys
 
@@ -24,22 +23,28 @@ def process_entries(entries):
     return out_lines
 
 def main(*paths):
-    """Reads dependency definitions from a (list of) file(s) or stdin and
-    removes hashes from returned entries"""
+    """
+    Reads dependency definitions from a (list of) file(s) provided on the
+    command line. If no command line arguments are present, data is read from
+    stdin instead.
+
+    Hashes are removed from returned entries.
+    """
 
     deps = []
-    for path in paths:
-        with open(path) as file_h:
-            deps += process_entries(file_h.readlines())
+    if paths:
+        for path in paths:
+            with open(path) as file_h:
+                deps += process_entries(file_h.readlines())
+    else:
+        # Need to check if interactive to avoid blocking if nothing is piped
+        if not sys.stdin.isatty():
+            stdin_data = []
+            for line in sys.stdin:
+                stdin_data.append(line)
+            deps += process_entries(stdin_data)
 
-    # Need to check if interactive to avoid blocking if nothing is piped
-    if not sys.stdin.isatty():
-        stdin_data = []
-        for line in sys.stdin:
-            stdin_data.append(line)
-        deps += process_entries(stdin_data)
-
-    return os.linesep.join(deps)
+    return "\n".join(deps)
 
 if __name__ == '__main__':
     print(main(*sys.argv[1:]))  # pylint: disable=star-args