diff --git a/CHANGELOG.md b/CHANGELOG.md
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -42,3 +42,8 @@
 ## 0.5.0.0 -- 2021-07-28
 
 * Fifth version. Added special data type and related parsing functionality to the module Rhythmicity.PolyRhythm.
+
+## 0.5.1.0 -- 2021-07-30
+
+* Fifth version revised A. Fixed issues with fixed point 1.0 for increasing and decreasing functions in the module
+Rhythmicity.PolyRhythm. 
diff --git a/Rhythmicity/PolyRhythm.hs b/Rhythmicity/PolyRhythm.hs
--- a/Rhythmicity/PolyRhythm.hs
+++ b/Rhythmicity/PolyRhythm.hs
@@ -218,6 +218,8 @@
 increasingF n x
  | n <= 0 || x <= 0 = error $ "Rhythmicity.PolyRhythm.increasingF: not defined for the arguments. " ++ show n ++ " " ++ show x
  | x < 1 = int2Double (n + 1) - int2Double n * x
+ | x <= 1.01 = x + (1.0 / int2Double n)
+ | n == 1 = x + 1.0
  | otherwise = x ^ n
 
 decreasingF
@@ -227,6 +229,8 @@
 decreasingF n x
  | n <= 0 || x <= 0 = error $ "Rhythmicity.PolyRhythm.decreasingF: not defined for the arguments. " ++ show n ++ " " ++ show x
  | x < 1 = x / int2Double n
+ | x <= 1.01 = x - (1.0 / int2Double n)
+ | n == 1 = x - 0.5
  | otherwise = x ** (1.0 / int2Double n)
 
 similarityF1
diff --git a/phonetic-languages-rhythmicity.cabal b/phonetic-languages-rhythmicity.cabal
--- a/phonetic-languages-rhythmicity.cabal
+++ b/phonetic-languages-rhythmicity.cabal
@@ -2,7 +2,7 @@
 -- For further documentation, see http://haskell.org/cabal/users-guide/
 
 name:                phonetic-languages-rhythmicity
-version:             0.5.0.0
+version:             0.5.1.0
 synopsis:            Allows to estimate the rhythmicity properties for the text
 description:         Allows to estimate (somewhat to say, evaluate) the rhythmicity properties for the text. Inspired by the ancient Greek and Latin poetry.