diff --git a/src/Extrema/Extrema_GExtPC.gxx b/src/Extrema/Extrema_GExtPC.gxx
index 59002f4f38..499aa6b663 100644
--- a/src/Extrema/Extrema_GExtPC.gxx
+++ b/src/Extrema/Extrema_GExtPC.gxx
@@ -118,7 +118,7 @@ void Extrema_GExtPC::Perform(const ThePoint& P)
 
       Standard_Integer anIdx;
 
-      // Find first and last used knot
+      // Find first and last used knot.
       Standard_Integer aFirstUsedKnot = aFirstIdx,
                         aLastUsedKnot = aLastIdx;
       for(anIdx = aFirstIdx; anIdx <= aLastIdx; anIdx++)
@@ -139,6 +139,16 @@ void Extrema_GExtPC::Perform(const ThePoint& P)
           break;
       }
 
+      if (aFirstUsedKnot == aLastUsedKnot)
+      {
+        // Degenerated case:
+        // Some bounds lies out of curve param space.
+        // In this case build one interval with [myuinf, myusup].
+        // Parameters of these indexes will be redefined.
+        aFirstUsedKnot = aFirstIdx;
+        aLastUsedKnot  = aFirstIdx + 1;
+      }
+
       mysample = (TheCurveTool::BSpline(aCurve))->Degree() + 1;
 
       // Fill sample points.