diff --git a/lib/http_signatures/http_signatures.ex b/lib/http_signatures/http_signatures.ex
index 15d7582..af88339 100644
--- a/lib/http_signatures/http_signatures.ex
+++ b/lib/http_signatures/http_signatures.ex
@@ -77,7 +77,7 @@ defmodule HTTPSignatures do
   end
 
   def sign(private_key, key_id, headers) do
-    sigstring = build_signing_string(headers, Map.keys(headers))
+    sigstring = build_signing_string(headers, Enum.sort(Map.keys(headers)))
 
     signature =
       :public_key.sign(sigstring, :sha256, private_key)
@@ -86,7 +86,7 @@ defmodule HTTPSignatures do
     [
       keyId: key_id,
       algorithm: "rsa-sha256",
-      headers: Map.keys(headers) |> Enum.join(" "),
+      headers: Map.keys(headers) |> Enum.sort() |> Enum.join(" "),
       signature: signature
     ]
     |> Enum.map_join(",", fn {k, v} -> "#{k}=\"#{v}\"" end)
diff --git a/mix.exs b/mix.exs
index a6a7cbc..a7bf8ae 100644
--- a/mix.exs
+++ b/mix.exs
@@ -8,7 +8,7 @@ defmodule HttpSignatures.MixProject do
     [
       app: :http_signatures,
       description: "Library for manipulating and validating HTTP signatures",
-      version: "0.1.1",
+      version: "0.1.2",
       elixir: "~> 1.7",
       elixirc_options: [warnings_as_errors: true],
       elixirc_paths: elixirc_paths(Mix.env()),
diff --git a/test/http_signatures_test.exs b/test/http_signatures_test.exs
index 27c0a26..3dbcdce 100644
--- a/test/http_signatures_test.exs
+++ b/test/http_signatures_test.exs
@@ -208,4 +208,30 @@ defmodule HttpSignaturesTest do
 
     assert HTTPSignatures.validate_conn(conn)
   end
+
+  test "Signatures are stable on OTP26+ with undefined Map.keys/1 ordering" do
+    user_ap_id = ~s|https://mastodon.social/users/lambadalambda#main-key|
+
+    # credo:disable-for-lines:10 Credo.Check.Readability.MaxLineLength
+    private_key =
+      {:RSAPrivateKey, :"two-prime",
+       28_756_005_415_572_484_042_763_333_825_843_542_309_845_812_712_410_557_401_080_975_665_944_065_546_687_053_162_744_064_118_733_269_231_397_398_437_337_112_118_822_093_392_471_512_223_279_218_516_015_781_047_498_524_701_011_344_834_660_702_300_339_866_912_903_829_480_780_711_421_965_266_995_321_160_936_070_443_834_148_409_010_341_833_400_730_167_696_056_399_186_720_243_079_891_586_296_037_178_998_225_766_461_225_833_387_132_735_728_367_079_742_073_397_917_419_922_243_432_508_105_117_797_420_565_462_233_617_076_268_056_263_255_047_301_378_690_482_484_074_947_841_896_587_287_731_635_988_553_127_288_143_474_145_525_724_255_965_068_001_976_777_796_779_533_346_344_982_614_532_834_052_163_179_471_788_571_859_959_462_813_779_224_935_806_760_043_776_072_659_926_191_283_296_091_970_506_062_030_984_091_470_929_266_003_011,
+       65_537,
+       25_233_957_481_263_615_321_105_929_907_140_426_297_194_450_296_637_489_603_371_636_030_768_012_109_037_222_140_003_526_671_473_370_973_612_835_255_371_123_456_268_345_987_778_455_955_579_105_800_632_735_218_909_015_602_715_449_920_523_322_539_825_529_794_789_191_349_004_359_581_262_836_335_214_000_723_765_372_612_446_022_890_653_506_246_486_594_506_922_860_631_830_586_989_403_926_452_005_709_205_303_322_232_716_957_756_646_692_607_039_707_869_476_684_696_402_780_134_400_419_892_792_178_031_077_409_586_563_911_414_056_442_023_360_496_531_178_932_232_960_305_935_443_131_268_902_698_561_476_776_016_479_175_692_849_949_462_150_713_017_077_076_502_024_471_442_627_225_940_981_940_235_409_308_119_456_929_193_383_984_043_313_294_569_986_326_805_396_849_905_695_401_341_785_041_176_269_677_759_870_702_155_638_035_216_833,
+       177_783_479_898_101_225_090_255_510_574_083_286_496_133_004_386_710_828_810_208_011_585_370_522_423_888_313_371_324_368_555_961_532_882_416_417_904_776_985_934_672_514_976_013_258_017_209_904_688_467_121_759_107_569_488_391_607_820_963_070_360_845_953_724_899_435_077_154_851_205_162_368_630_793_919_412_726_847_267_327_206_524_298_869_094_621_709_415_910_252_626_752_919_831_010_415_748_000_011_171_076_295_507,
+       161_747_342_509_294_677_375_914_222_076_718_822_400_941_009_725_673_497_592_218_662_627_801_812_486_196_781_966_854_364_060_860_604_565_261_653_867_622_254_133_771_945_941_570_294_029_162_561_824_060_451_304_312_080_304_336_296_778_308_854_167_291_375_658_502_471_854_680_814_450_977_871_287_689_807_234_161_418_665_899_011_960_362_411_939_434_739_945_865_837_893_017_653_193_120_275_492_634_544_890_342_133_073,
+       123_805_792_744_090_236_231_352_842_624_633_216_540_229_399_990_922_616_477_243_136_560_183_183_131_724_655_293_252_252_262_470_488_414_492_620_912_707_582_908_471_838_976_307_567_979_117_793_613_942_520_560_353_851_471_393_328_796_571_914_616_150_395_685_653_681_393_507_030_443_145_175_121_546_663_534_758_084_477_982_611_022_208_463_716_823_171_582_964_249_502_302_157_684_475_706_308_237_675_051_295_467_455,
+       43_886_525_847_998_503_945_839_856_828_481_836_213_643_179_195_598_305_296_013_431_479_127_391_086_402_355_569_138_109_796_454_266_603_284_903_628_088_849_398_152_688_446_724_796_197_973_185_747_828_599_800_010_336_328_664_846_259_546_333_289_634_484_977_333_276_691_333_662_550_426_301_283_819_829_290_902_213_203_488_353_612_145_267_697_743_695_099_217_027_471_712_771_550_117_715_775_974_296_614_737_687_265,
+       90_283_918_084_263_940_362_515_004_232_322_731_054_469_960_381_679_586_824_438_807_054_374_237_285_157_945_298_098_405_267_918_780_650_461_768_149_536_719_331_445_672_754_509_549_303_377_662_269_991_550_734_109_336_424_702_266_640_645_630_618_719_389_738_627_119_442_677_159_263_798_411_854_553_104_387_445_904_992_891_045_248_551_150_818_831_926_648_119_173_927_771_126_688_710_466_061_199_827_928_052_600_203,
+       :asn1_NOVALUE}
+
+    headers = %{host: "test.test", "content-length": 100}
+
+    expected_signature =
+      ~s|keyId="https://mastodon.social/users/lambadalambda#main-key",algorithm="rsa-sha256",headers="content-length host",signature="sibUOoqsFfTDerquAkyprxzDjmJm6erYc42W5w1IyyxusWngSinq5ILTjaBxFvfarvc7ci1xAi+5gkBwtshRMWm7S+Uqix24Yg5EYafXRun9P25XVnYBEIH4XQ+wlnnzNIXQkU3PU9e6D8aajDZVp3hPJNeYt1gIPOA81bROI8/glzb1SAwQVGRbqUHHHKcwR8keiR/W2h7BwG3pVRy4JgnIZRSW7fQogKedDg02gzRXwUDFDk0pr2p3q6bUWHUXNV8cZIzlMK+v9NlyFbVYBTHctAR26GIAN6Hz0eV0mAQAePHDY1mXppbA8Gpp6hqaMuYfwifcXmcc+QFm4e+n3A=="|
+
+    signature = HTTPSignatures.sign(private_key, user_ap_id, headers)
+
+    assert signature == expected_signature
+  end
 end