diff --git a/engines/LuaCommon/lualib/ustring/ustring.lua b/engines/LuaCommon/lualib/ustring/ustring.lua
index da757e8b..c6462177 100644
--- a/engines/LuaCommon/lualib/ustring/ustring.lua
+++ b/engines/LuaCommon/lualib/ustring/ustring.lua
@@ -740,11 +740,10 @@ end
 --    inside brackets and aren't followed by quantifiers and aren't part of a
 --    '%b', but that's too complicated to check.
 --  * If it contains a negated character set.
---  * If it contains "%a" or any of the other %-prefixed character sets except
---    %z or %Z.
---  * If it contains a '.' not followed by '*', '+', or '-'. A bare '.' or '.?'
---    would try to match a partial UTF-8 character, but the others will happily
---    enough match a whole character thinking it's 2 or 4.
+--  * If it contains "%a" or any of the other %-prefixed character sets except %z.
+--  * If it contains a '.' not followed by '*', '+', '-'. A bare '.' or '.?'
+--    matches a partial UTF-8 character, but the others will happily enough
+--    match a whole UTF-8 character thinking it's 2, 3 or 4.
 --  * If it contains position-captures.
 --
 -- @param string pattern
@@ -753,8 +752,8 @@ local function patternIsSimple( pattern )
 	return not (
 		S.find( pattern, '[\128-\255]' ) or
 		S.find( pattern, '%[%^' ) or
-		S.find( pattern, '%%[acdlpsuwxACDLPSUWX]' ) or
-		S.find( pattern, '%.[^*+-]' ) or
+		S.find( pattern, '%%[acdlpsuwxACDLPSUWXZ]' ) or
+		S.find( pattern, '%.[^*+-]' ) or S.find( pattern, '%.$' ) or
 		S.find( pattern, '()', 1, true )
 	)
 end
diff --git a/tests/engines/LuaCommon/UstringLibraryTests.lua b/tests/engines/LuaCommon/UstringLibraryTests.lua
index d0a415f9..5a382265 100644
--- a/tests/engines/LuaCommon/UstringLibraryTests.lua
+++ b/tests/engines/LuaCommon/UstringLibraryTests.lua
@@ -511,6 +511,34 @@ return testframework.getTestProvider( {
 	  args = { str2, 'f%a+', { ['főó'] = 'Y', ['foó'] = 'Z' }, 1 },
 	  expect = { str2, 1 }
 	},
+	{ name = 'gsub: (inverted zero character class)', func = mw.ustring.gsub,
+	  args = { "ó", '%Z', 'repl' },
+	  expect = { 'repl', 1 }
+	},
+	{ name = 'gsub: (single dot pattern at end)', func = mw.ustring.gsub,
+	  args = { "ó", '.', 'repl' },
+	  expect = { 'repl', 1 }
+	},
+	{ name = 'gsub: (single dot pattern at end + leading)', func = mw.ustring.gsub,
+	  args = { 'fó', 'f.', 'repl' },
+	  expect = { 'repl', 1 }
+	},
+	{ name = 'gsub: (dot pattern)', func = mw.ustring.gsub,
+	  args = { 'f ó b', 'f . b', 'repl' },
+	  expect = { 'repl', 1 }
+	},
+	{ name = 'gsub: (dot pattern with +)', func = mw.ustring.gsub,
+	  args = { 'f óóó b', 'f .+ b', 'repl' },
+	  expect = { 'repl', 1 }
+	},
+	{ name = 'gsub: (dot pattern with -)', func = mw.ustring.gsub,
+	  args = { 'f óóó b', 'f .- b', 'repl' },
+	  expect = { 'repl', 1 }
+	},
+	{ name = 'gsub: (dot pattern with *)', func = mw.ustring.gsub,
+	  args = { 'f óóó b', 'f .* b', 'repl' },
+	  expect = { 'repl', 1 }
+	},
 	{ name = 'gsub: (function 1)', func = mw.ustring.gsub,
 	  args = { str2, 'f%a+', function(m) if m == 'fo' then return nil end return '-' .. mw.ustring.upper(m) .. '-' end },
 	  expect = { '-FOO- bar -FŐÓ- -FOÓ- baz -FOOOO- -FOOFOO- fo', 6 }