diff -r ec0af9c59270 -r 1a1972b1a1ff mercurial/hgweb/webcommands.py
--- a/mercurial/hgweb/webcommands.py	Sat Mar 10 12:35:38 2018 -0800
+++ b/mercurial/hgweb/webcommands.py	Sat Mar 10 11:46:52 2018 -0800
@@ -762,8 +762,8 @@
     basectx = ctx.p1()
 
     style = web.config('web', 'style')
-    if 'style' in req.form:
-        style = req.form['style'][0]
+    if 'style' in req.req.qsparams:
+        style = req.req.qsparams['style']
 
     diffs = webutil.diffs(web, tmpl, ctx, basectx, [path], style)
     if fctx is not None:
@@ -1011,8 +1011,8 @@
     entries = []
 
     diffstyle = web.config('web', 'style')
-    if 'style' in req.form:
-        diffstyle = req.form['style'][0]
+    if 'style' in req.req.qsparams:
+        diffstyle = req.req.qsparams['style']
 
     def diff(fctx, linerange=None):
         ctx = fctx.changectx()