diff --git a/Lib/booleanOperations/flatten.py b/Lib/booleanOperations/flatten.py
index 8f1d7e1..942bed6 100644
--- a/Lib/booleanOperations/flatten.py
+++ b/Lib/booleanOperations/flatten.py
@@ -953,18 +953,23 @@ class OutputPoint(InputPoint):
 
 def _tValueForPointOnCubicCurve(point, cubicCurve, isHorizontal=0):
     """
-    Finds a t value on a curve from a point.
-    The points must be originaly be a point on the curve.
-    This will only back trace the t value, needed to split the curve in parts
+    Finds a t-value on a curve from a point.
+    The point must be originally be on the curve.
+    This will only backtrace the t value, needed to split the curve in parts
     """
     pt1, pt2, pt3, pt4 = cubicCurve
     a, b, c, d = bezierTools.calcCubicParameters(pt1, pt2, pt3, pt4)
-    solutions = bezierTools.solveCubic(a[isHorizontal], b[isHorizontal], c[isHorizontal],
-        d[isHorizontal] - point[isHorizontal])
-    solutions = [t for t in solutions if 0 <= t < 1]
+    solutions = bezierTools.solveCubic(
+        a[isHorizontal],
+        b[isHorizontal],
+        c[isHorizontal],
+        d[isHorizontal] - point[isHorizontal]
+    )
+    solutions = [t for t in solutions if 0 <= t <= 1]
     if not solutions and not isHorizontal:
-        # can happen that a horizontal line doens intersect, try the vertical
-        return _tValueForPointOnCubicCurve(point, (pt1, pt2, pt3, pt4), isHorizontal=1)
+        # If the horizontal line doesn't intersect, try the vertical
+        return _tValueForPointOnCubicCurve(point, (pt1, pt2, pt3, pt4),
+                                           isHorizontal=1)
     if len(solutions) > 1:
         intersectionLenghts = {}
         for t in solutions: