diff --git a/Misc/NEWS b/Misc/NEWS
index 9fc2ca99b61..77bc70060a7 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -759,6 +759,8 @@ Tests
 Tools/Demos
 -----------
 
+- Issue #18974: Tools/scripts/diff.py now uses argparse instead of optparse.
+
 - Issue #21906: Make Tools/scripts/md5sum.py work in Python 3.
   Patch by Zachary Ware.
 
diff --git a/Tools/scripts/diff.py b/Tools/scripts/diff.py
index 8be527fd627..9720a431557 100755
--- a/Tools/scripts/diff.py
+++ b/Tools/scripts/diff.py
@@ -8,7 +8,7 @@
 
 """
 
-import sys, os, time, difflib, optparse
+import sys, os, time, difflib, argparse
 from datetime import datetime, timezone
 
 def file_mtime(path):
@@ -18,23 +18,25 @@ def file_mtime(path):
 
 def main():
 
-    usage = "usage: %prog [options] fromfile tofile"
-    parser = optparse.OptionParser(usage)
-    parser.add_option("-c", action="store_true", default=False, help='Produce a context format diff (default)')
-    parser.add_option("-u", action="store_true", default=False, help='Produce a unified format diff')
-    parser.add_option("-m", action="store_true", default=False, help='Produce HTML side by side diff (can use -c and -l in conjunction)')
-    parser.add_option("-n", action="store_true", default=False, help='Produce a ndiff format diff')
-    parser.add_option("-l", "--lines", type="int", default=3, help='Set number of context lines (default 3)')
-    (options, args) = parser.parse_args()
-
-    if len(args) == 0:
-        parser.print_help()
-        sys.exit(1)
-    if len(args) != 2:
-        parser.error("need to specify both a fromfile and tofile")
+    parser = argparse.ArgumentParser()
+    parser.add_argument('-c', action='store_true', default=False,
+                        help='Produce a context format diff (default)')
+    parser.add_argument('-u', action='store_true', default=False,
+                        help='Produce a unified format diff')
+    parser.add_argument('-m', action='store_true', default=False,
+                        help='Produce HTML side by side diff '
+                             '(can use -c and -l in conjunction)')
+    parser.add_argument('-n', action='store_true', default=False,
+                        help='Produce a ndiff format diff')
+    parser.add_argument('-l', '--lines', type=int, default=3,
+                        help='Set number of context lines (default 3)')
+    parser.add_argument('fromfile')
+    parser.add_argument('tofile')
+    options = parser.parse_args()
 
     n = options.lines
-    fromfile, tofile = args
+    fromfile = options.fromfile
+    tofile = options.tofile
 
     fromdate = file_mtime(fromfile)
     todate = file_mtime(tofile)